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Tailoring catalyst-ionomer and electrolyte interaction is crucial for the development of anion exchange membrane (AEM) water electrolysis. In this work, the interaction of Ni-MoO2 nanosheets with ionomers and electrolyte cations was investigated. The activity of Ni-MoO2 nanosheets for the hydrogen evolution reaction (HER) increased when tested in 1 M NaOH compared to 1 M KOH; however, it decreased when tested in 0.01 M KOH compared to 1 M KOH electrolyte. The capacitance minimum associated with the potential of zero free charge (pzfc) was shifted negatively from 0.5 to 0.4 V versus RHE when KOH concentration increased from 0.1 mM to 1 M KOH, suggesting a softening of the water in the double-layer to facilitate the OH- transport and faster kinetics of the Volmer step that lead to improved HER activity. The catalyst interaction with cationic moieties in the anion ionomer (or organic electrolytes) can also be rationalized based on the capacitance minimum, because the latter indicates a negatively charged catalyst during the HER, attracting the cationic moieties leading to the blocking of the catalytic sites and lower HER performance. The HER activity of Ni-MoO2 nanosheets is lower in benzyltrimethylammonium hydroxide (BTMAOH) than in tetramethylammonium hydroxide (TMAOH). Anion fumion ionomer and electrolytes with organic cations with benzyl group adsorption (such as BTMAOH) lead to decreased HER activity in comparison with TMAOH and Nafion. By utilizing Ni-MoO2 nanosheet electrodes as a cathode in a full non-platinum group metal (PGM) AEM electrolyzer, a current density of 1.15 A/cm2 at 2 V cell voltage in 1 M KOH at 50 °C was achieved. The electrolyzer showed exceptional stability in 0.1 M KOH for 65 h at 0.5 A/cm2.

A novel sonochemical approach to synthesize platinum (Pt) nanoparticles has been developed to produce smaller, and more monodisperse particles than traditional chemical reduction methods such as the sodium borohydride (NaBH4) reduction method. It was also found that careful experimental manipulation of the ultrasonic conditions such as the ultrasonic frequency (f), the acoustic power (Pacoustic) and the solution volume (V) may be employed to tailor the sonochemical radical yield to the same value for two different ultrasonic systems (20 kHz provided by an ultrasonic probe or sonifier, and 408 kHz by an ultrasonic plate transducer) leading to a similar reduction rate, and as a consequence, to Pt-nanoparticles with similar sizes. The reduction of Pt(IV) was found to be a first order reaction with a rate constant (k) of 0.062 min−1 for both ultrasonic systems, and the particle sizes from TEM measurements were found to be (2.2 ± 0.5) nm and (2.3 ± 0.4) nm for the 20 kHz and the 408 kHz samples, respectively. In comparison, the chemical reduction method resulted in particle sizes of (3.0 ± 0.5) nm. It was also found that the sonochemical synthesis at 408 kHz was more efficient than at 20 kHz with an initial sonochemical efficiency of (0.20 ± 0.04) μmol kJ−1 at 408 kHz and (0.060 ± 0.004) μmol kJ−1 at 20 kHz. The sonochemical synthesis at 408 kHz also yielded nanoparticles of higher purity. Interestingly, direct sonication into the reaction vessel using the 20 kHz sonication probe produced impurities of Ti, V and Al in the solution, indicating that direct sonication at lower frequencies led to (i) probe material (made of Ti alloy – Ti-6Al-4V) erosion induced by cavitation and (ii) a continuous supply of micro meter sized impurities. It was also observed that the introduction of impurities increased the reduction rate constant of Pt(IV) through heterogeneous nucleation (k = 0.12 min−1) as was demonstrated for the 408 kHz system under controlled addition of Ti/Al/V seed microparticles. Direct sonication using a sonifier should therefore be avoided when high purity catalytic materials are required.

Developing scalable synthetic routes for fabricating low‐cost CO‐tolerant and highly active electrocatalysts have significant relevance for fuel cell applications. Here, we report a novel and rapid single step synthesis of Ni enriched bimetallic core‐shell (Ni−Pt) rhombic dodecahedra nanoparticles (NPs) via the thermal decomposition of precursor in the presence of oleylamine. Electrochemical dealloying in acidic medium (0.1 M HClO4) subjecting NPs to different potential cycles is employed to vary the chemical composition and morphologies of parent bimetallic core‐shell NPs. As a result, rhombic dodecahedra NPs transform to different morphologies such as concave, nanocage (open structure), and squeezed nanocage. Our results reveal that concave rhombic dodecahedra shaped electrocatalysts show high resistance to CO poisoning compare to core‐shell, nanocage, and squeezed nanocage morphologies as well as commercial Pt/C electrocatalysts. The improved CO tolerant of concave rhombic dodecahedra bimetallic NPs results from the presence of optimal content of Ni along with Pt content at the surface. We also demonstrate that CO tolerance of concave bimetallic NPs can be changed by electrochemical parameters such as the scan rate and CO adsorption potential. Overall, the present study presents a conceptual strategy for achieving improved CO tolerance by change in the composition and morphologies of bimetallic core‐shell NPs. Marked Open Access

Rational design of efficient, earth-abundant, and durable electrocatalysts to accelerate the oxygen evolution reaction (OER) is critical for hydrogen ion by water electrolysis. In the present work, nanostructured Ni12−xFexP5 (x = 1.2, 2.4, 3.6) OER electrocatalysts synthesized by a colloidal method is reported. For x = 1.2, an alloy of Ni, Fe, and P is formed. For x = 2.4 or x = 3.6, a core-shell NiFeP@Fe3O4 structure is formed. The nanoparticles are encapsulated in a self-generated carbon layer. The carbon layer is formed during synthesis from synthesis residues. The carbon-encapsulated Ni9.6Fe2.4P5 catalyst offers the outstanding mass activity of 0.1 A mg−1 and overpotential of 220 mV at 10 mA cm−2, assigned to a combination of enhanced electrical conductivity provided by the carbon shell, a large surface area, and a high specific catalytic activity. Post-mortem characterization indicates that the carbon encapsulation remains intact under conditions of the OER.

A novel bi-layer coating composed of a tantalum base layer with an Indium Tin Oxide (ITO) top layer was applied to titanium substrates. Samples were polarized ex situ in a parameter study, where the pH, potential and temperature of the electrolyte was altered, as well as the polarization duration. The Interfacial Contact Resistance (ICR) after polarization showed an increase with time for the first 24 h, then stabilized at approx. 30 mΩ cm2. Minor variations were seen in the ICR after polarization at 1.4 VRHE and 2.0 VRHE, but after polarization at 2.5 VRHE and 2.6 VRHE, the ICR increased to 102 mΩ cm2 and 503 mΩ cm2, respectively. X-ray photoelectron spectroscopy (XPS) analysis revealed that the oxygen to metal ratio on the Tantalum- Indium Tin Oxide (Ta-ITO) coated sample surfaces increased with increasing polarization potential. The surfaces of the samples polarized at 2.5 VRHE and 2.6 VRHE showed lower concentrations of oxygen vacancies, an increase in hydroxides and a decrease in metallic character compared to the non-coated and baseline samples. ITO proved to be a promising candidate for use as coating on BiPolar Plates (BPPs) in Proton Exchange Membrane Water Electrolyzers (PEMWEs). © 2022 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY- NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: permissions@ioppublishing.org.

There is a strong desire to replace bulk nickel electrodes for oxygen evolution reaction (OER) with a cheaper and more active steel material in alkaline water electrolyser (AWE). However, implementing an activation procedure to optimize the steel electrode surface is necessary. In this work, we activated 316 stainless steel (SS316) in KOH electrolytes of increasing concentration by applying an optimized potential of +1.70 V vs RHE for 18 hours. The electrocatalytic activity increased significantly with increasing the KOH concentration of the activation electrolyte, which is linked to a beneficial change in the surface composition during activation. The surface was analysed using X-ray Photoelectron Spectroscopy (XPS), Glow Discharge - Optical Emission Spectroscopy (GD-OES) and Scanning Electron Microscopy (SEM). XPS showed an increasing Ni content (41% to 73%) in the surface with simultaneous removal of Cr (3.4% to 0%) and Fe (55% to 27%) with increasing KOH concentration of the activation electrolyte. Activation in minimum 7.5 M KOH gave the best performing OER electrode with an electrode potential (E) of +1.525 V vs. RHE at a current density (j) of 10 mA cm-2. Tafel slopes of around 40 mV dec-1 were found for all activated samples, indicating the same OER mechanism independent of the resulting surface composition. Reaction orders of 1.5 and 1.3 were found in the low and high potential regions, respectively. A negligible performance change was observed for the activated electrodes over a 48 h test at 10 mA cm-2 in 1.0 M KOH. This work shows that the electrochemical activation of 316 stainless steel in high pH KOH electrolytes improves the OER activity significantly and that the surface composition can be tailored with KOH concentration up to 73% Ni. Through optimizing the surface composition, steel materials offer a cost-effective alternative to bulk nickel electrodes as OER electrodes in commercial AWE.

As the proton exchange membrane fuel cell (PEMFC) has improved its performance and power density, the efficiency has remained unchanged. With around half the reaction enthalpy released as heat, thermal gradients grow. To improve the understanding of such gradients, PEMFC component thermal conductivity has been increasingly investigated over the last ten years, and the catalyst layer (CL) is one of the components where thermal conductivity values are still scarce. CLs in PEMFC are where the electrochemical reactions occur and most of the heat is released. The thermal conductivity in this region affects the heat distribution significantly within a PEMFC. Thermal conductivities for a graphitized and a non-graphitized CL were measured for compaction pressures in the range of 3 and 23 bar. The graphitized CL has a thermal conductivity of 0.12 ± 0.05 WK–1m–1, whilst the non-graphitized CL conductivity is 0.061 ± 0.006 WK–1m–1, both at 10 bar compaction pressure. These results suggest that the graphitization of the catalyst material causes a doubling of the thermal conductivity of the CL. This important finding bridges the very few existing studies. Additionally, a 2D thermal model was constructed to represent the impact of the results on the temperature distribution inside a fuel cell.

Iridium oxide powders with a surface area of more than 1 m2 g-1 (4 m2 g-2 from the H-UPD charge) and iridium-oxide crystallites less than 10 nm across were synthesized by heat treating gels formed from citric acid, ethylene glycol and dihydrogen hexachloroiridate(iv) in air. The characteristics of the resulting material was found to be strongly dependent on the heat-treatment step in the synthesis. A single heat-treatment of the gel resulted in a material with a substantial fraction of elemental iridium metal, i.e. iridium in oxidation state zero (Ir0). Post-synthesis modification of the powder by potential cycling resulted in oxidation peaks consistent with the conversion of the metal phase to iridium oxide. Linear combination of the near-edge part of the X-ray absorption data (X-ray absorption near-edge spectroscopy, XANES) collected in situ during potential cycling and an analysis of the extended X-ray fine-structure (EXAFS) part of the spectrum showed that the overall metal fraction was not significantly affected by the cycling. The oxidation of the metal phase is therefore limited to a thin layer of oxide at the metal surface, and a significant part of the iridium is left inactive. A modification of the heat treatment procedure of the sample resulted in iridium oxide containing only insignificant amounts of elemental iridium metal.

Water electrolyzers that use a membrane electrolyte between the electrodes are a promising technology towards mass production of renewable hydrogen. High power setups produce a lot of heat which has to be transported through the cell, making heat management essential. Knowing thermal conductivity values of the employed materials is crucial when modeling the temperature distribution inside an electrolyzer. The thermal conductivity was measured for different titanium-based porous transport layers (PTL) and a partially methylated Hexamethyl-p-Terphenyl Polybenzimidazolium (HMT-PMBI-Cl- membrane. The four titanium-based sintered transport layers materials have thermal conductivities between 1.0 and 2.5 0.2 WK−1m−1 at 10 bar compaction pressure. The HMT-PMBI-Cl- membrane has a thermal conductivity of 0.19 0.04 WK−1m−1 at 0% relative humidity at 10 bar compaction pressure and 0.21 0.03 WK−1m−1 at 100% relative humidity ( water molecules per ion exchange site at room temperature) at 10 bar compaction pressure. Combining the determined thermal conductivity values with data from the literature, 2D thermal models of a proton exchange membrane water electrolyzer (PEMWE) and an anion exchange membrane water electrolyzer (AEMWE) were built to evaluate the temperature distribution in the through-plane direction. A temperature difference of 7–17 K was shown to arise between the center of the membrane electrode assembly and bipolar plates for the PEMWE and more than 18 K for the AEMWE. This is an open access article distributed under the terms of the Creative Commons CC-BY license, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Fuel cells capable of synthetic glucose catalysis have revolved around the implementation of abiotic catalysts that require extreme acid and alkaline environments. These are not compatible with implantable medical sensor systems, and hence, there is a need to develop abiotic catalysts that operate at neutral pH. This paper presents structural and electrochemical characteristics of a nanoporous electrode designed for abiotic glucose oxidation in the presence of oxygen in neutral physiological media. The electrode was fabricated by annealing e-beam deposited thin films of platinum (Pt) and nickel (Ni) into a Pt–Ni alloy on a silicon substrate. The porous nature of the alloy enhances electrochemical properties by increasing the real surface area ~ 500 times compared to the geometric surface area of as-prepared multilayer thin films. This was reflected in the exchange current density of the electrode annealed at 800 °C being twice that of the electrode annealed at 650 °C. The cell voltage increase, due to the addition of dissolved physiological oxygen of 2 ppm, was about 100 ± 8 mV under a load current density of 2 µA cm−2. After running for 72 h in a physiological saline solution with 5 mM glucose, the increase in the electrode potential was only 23 µV h−1. These results suggest that the nanoporous Pt–Ni alloy anode offers an improved catalytic stability with time and should be a viable candidate for use in abiotic catalyzed glucose fuel cell systems operating under physiological conditions.

In the present work, the crystallization of anatase TiO₂ nanoparticles (NPs), using different ferrite nanoparticles with different chemical composition, dimensions and shape as nucleation seeds, was investigated. In particular, CoFe₂O₄, NiFe₂O₄ and Fe₃O₄ NPs with a volume ratio equal to 1:1000 with respect of TiO₂ amount, were used in order to investigate the synthesis of nanocrystalline tetragonal anatase TiO₂ by a hydrothermal synthesis. In addition, Lu₂O₃ nanoparticles were also used to detect the effect of a non-magnetic nanoparticle on the synthesis and nanocrystallization of titania. For each sample, a deep physical characterization was performed by XRD (with a Rietveld refinement of the structural data), FE-SEM, STEM, HRTEM, DSC analysis and BET surface area measurement. Furthermore, for some samples, the photocatalytic activity was investigated by degradation of methylene blue in aqueous medium, in the framework of a standard ISO 10678:2010 protocol. The hydrothermal synthesis was performed with a 3 hours' thermal treatment, at a pressure of approximatively 9 bar and a temperature significantly lower (Tmax═150 °C) than the usual temperature necessary to obtain crystalline anatase TiO₂ (Tcryst═350 °C). The results give evidence that the mere presence of a nucleation seeds in the hydrothermal reactor, without any particular need for the composition and morphology, leads to crystalline anatase TiO₂ nanoparticles with high photocatalytic performances.

The effect of applying sandblasting during pretreatment while preparing titanium based IrO 2 − Ta 2 O 5 anodes by the conventional method was investigated. It was observed that sandblasting influences the surface morphology both before and after coating as deeper and smaller etching pits are obtained on the substrate before coating process and rougher surface is obtained after coating. As a result larger outer electrochemical active surface area (ECSA) is obtained on the anodes with sandblasting, which was determined based on cyclic voltammetry, whereas the inner ECSA is independent of the pretreatment. The polarization measurements in a quasi-steady state reveal that sandblasting has slight influence on the catalytic activity. Accelerated lifetime tests were carried out in acidic 0.9 mol L−1 Na2SO4 solution (pH = 2) at a current density of 5 × 107 A cm−2 under galvanostatic conditions. It shows that sandblasting would shorten the lifetime of the anode due to oxidation of the titanium substrate. This is suggested to be due to the shorter distance between the lowest spot of the outer coating surface and the highest spot of the outer substrate of the anode after applying sandblasting in titanium substrate pretreatment.

To improve the performance of electrochemical hydrogen conversion devices such as electrolyzers and fuel cells, more efficient catalyst materials must be developed. As the available surface area is key to the performance of a catalyst, high surface area nanoparticles are required. The synthesis of such nanostructured catalysts is predominantly based on chemical reduction with a strong reducing agent like sodium borohydride. However, it is difficult to achieve the desired particle properties without the use of additives such as surfactants or stabilizers. In order to achieve more control over the nucleation and growth stage of the nanoparticles, we can replace the chemical reduction route by sonochemical reduction. In sonochemistry, high power ultrasound is used to generate reducing radicals which allow for controlled reduction of metal precursors. The radical generation rate is strongly linked to the nucleation and growth of the resulting nanoparticles and can easily be tuned by adjusting the ultrasonic frequency and power. Ultrasound therefore offers an easy and reproducible way of tuning the size of nanoparticles. In our work we have compared the size, shape, and morphology of Pt-nanoparticles synthesized sonochemically and with chemical reduction to see if the sonochemical route indeed offers better control during nucleation and growth. TEM-images along with X-ray diffractograms revealed that the sonochemical route gives smaller and more monodisperse particles compared to chemical reduction. In addition, the particle shape was found to be spherical with the sonochemical route, whereas chemical reduction resulted in many different shapes. The better and easier control over synthesis parameters exhibited by the sonochemical route can therefore be utilized to produce nanoparticles of very similar physical properties. We also showed that the catalytic properties of these nanoparticles towards hydrogen evolution were very similar further strengthening the sonochemical route when it comes to development of catalyst materials. A comparison between high frequency (408 kHz) and low frequency (20 kHz) ultrasound was also made to determine the impact of the higher mechanical effects expected at lower frequencies. No significant differences in particle size and morphology were found, but agglomerate sizes were found to decrease at lower frequencies. In addition, it was found that extensive probe erosion occurs at 20 kHz resulting in contamination of the nanoparticle solution. In fact, it was shown that the eroded particles act as nucleation sites for Pt-nanoparticles and increased reduction rates were observed. No such particle erosion happened at higher frequencies which led us to conclude that direct sonication at low ultrasonic frequencies in general must be avoided to prevent contamination of your system. This is important in all applications of low frequency (20 kHz) ultrasound, whether it be sonochemistry, dispersion of colloids, or ink preparation for electrochemical characterization.

To succeed with the green transition, one must have cheap and reliable ways to store intermittent renewable energy. It is believed that hydrogen will play a key role in this regard, preferably through electrochemical water splitting. Alkaline water electrolysis is a mature technology, using nickel materials in most key components. Although Ni and Ni-S are active materials towards the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively, it is desirably to develop more active, durable and cheaper electrodes through a simple activation procedure of low-Ni containing materials. Moureaux et al. [1, 2] and Schäfer et al. [3] have shown that cheap stainless steel electrodes can be activated through electrooxidation in high pH electrolytes creating a nickel enriched surface. In this work we have employed a similar activation procedure, activating SS316 at 1.7 V for 18 hours at room temperature in a 3-electrode electrochemical cell using electrolytes with various KOH concentrations. The surface composition was analyzed with XPS and GD-OES before and after activation, and revealed that the Ni content in the surface increased with increasing KOH, at the expense of Fe and Cr. The composition converged to 73% Ni and 27% Fe for KOH concentration of 7.5 and higher. This composition showed the best OER performance of all surfaces prepared, including pure Ni electrodes. A similar enrichment of Ni was observed for SS304, reaching the same surface composition as SS316. However, the Ni content in the surface after activation changed less and was lower than SS316 and SS304 after activation for plate materials with higher nominal Ni bulk composition (Inconel718, Incoloy800 and NiFe 50:50 alloy). Hence, the surface composition can be tuned by selecting an electrode material and pH of the activation electrolyte. Furthermore, we have tested the activated SS316 electrodes at relevant operating conditions in a single cell alkaline water electrolyzer test rig (30wt% KOH, 80°C and 9 bar) and compared it with Ni and as-received SS316 electrodes. The activated SS316 electrodes outperformed the other electrodes and showed a stable performance during 255 hours operation at 0.8 A cm-2. The OER electrode activation procedure was successfully attempted in-situ in the alkaline single cell water electrolyzer test rig. However, the application of high currents needed for the activation led to high cell voltages (3 V) and hence harmful conditions. Finally, the effect of the activation procedure on the HER performance was also investigated and tied to the purity of the electrolyte. Deposition of Cu and Fe metal impurities was observed on the HER electrode, which increased with a lower grade of the KOH electrolyte. HER activity was observed to increase after activation in low grade KOH, which was attributed to an increased surface area and higher Fe to Cu ratio in the deposit. [1] F. Moureaux, P. Stevens, G. Toussaint, M. Chatenet, J. Power Sources 229 (2013) 123-132. [2] F. Moureaux, P. Stevens, G. Toussaint, M. Chatenet, Appl. Catal. B-Environ 258 (2019) 117963. [3] H. Schäfer, D.M. Chevrier, P. Zhang, J. Stangl, K. Müller‐Buschbaum, J.D. Hardege, K. Kuepper, J. Wollschläger, U. Krupp, S. Dühnen, Adv. Funct. Mater. 26 (2016) 6402-6417.

We report on the optimization of nickel-copper catalysts for superior performance as a cathode catalyst in anion exchange membrane (AEM) water electrolysis. The bifunctional system of NiCu mixed metal oxide (MMO) nanosheets includes Ni metallic, NiO, and CuO oxides provide rapid kinetics for the hydrogenevolution reaction (HER) of the Volmer step. In-situ Raman spectroscopy for NiCu MMO proved that nickel hydroxide was sustained under HER conditions for at least 30,000 s, which may explain why the exceptional activity of NiCu MMO as compared to other nickel-copper catalysts is maintained over time. The activity of the NiCu MMO for the HER activity in alkaline electrolytes increased as KOH concentration raised from 0.1 M to 1 M. The NiCu MMO nanosheets showed superior stability under alkaline HER conditions for 30 h. The use of Nafion ionomer in the ink resulted in a higher HER current density as compared to inks with a Fumion anion ionomer. The maximum HER performance was achieved at a Nafion ionomer to catalyst weight ratio of 0.5. Using Ir black as the anode, the NiCu MMO cathode gave an AEM electrolyzer performance of 1.85 A/cm2 at 2 V in 1 M KOH at 50 °C. The NiCu MMO catalyst developed here delivers AEM performance comparable to PEM water electrolysis. © 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

Iridium and ruthenium oxide are active electrocatalysts for oxygen evolution. The relation between preparation method, structure, and behavior of mixed oxides of iridium and ruthenium are of interest in order to obtain active and stable catalysts. In this work the structure of mixed Ru–Ir oxides synthesized by the polymeric precursor method, which involves the formation of a gel containing the metal precursors and subsequent heat-treatment in air, was studied for the IrxRu1−xO2 system. An in-depth analysis of X-ray diffraction (XRD) and X-ray absorption (XAS) data, including EXAFS and linear combination of XANES, shows that the polymeric precursor synthesis method is capable of providing an intimate mixing of Ir and Ru in the catalyst. In addition to the oxide phase, metal phases, i.e. with Ru or Ir or both in oxidation state zero (Ir(fcc) and Ru(hcp)), were also found in the product materials. Facing complex structures such as some of those synthesized here, we have shown that a representation of shells with more than one atom type are efficiently represented using mixed sites, i.e. including scattering contributions from several elements in a site corresponding to a partial occupancy of the site by these elements, this method forming a very efficient basis for analyzing EXAFS data.

Electrocatalysis of the oxygen reduction reaction (ORR), oxidation of carbon monoxide, and the methanol oxidation reaction (MOR) are all critical to the performance of direct-methanol fuel cells (DMFC). In this work we analysed the activity and mechanism for these reactions at carbon-supported Ru@Pt core-shell catalysts based on measurements of the potential of zero total charge (PZTC) and cyclic voltammetry. The PZTC measured at Ru@Pt is approximately 140 mV lower than at Pt. An analysis of charging curves and complex-capacitance data shows that the lower PZTC cannot be explained exclusively by a lower potential of zero free charge (PZFC). The lower PZTC at the core-shell catalyst therefore indicates that OH adsorbs more strongly on the Ru@Pt than on Pt. From a scaling relation between the free energies of adsorbed oxygen and OH we infer that the lower PZTC value for Ru@Pt implies a larger potential-determining step for the ORR at this catalyst than at Pt. For oxidation of CO and the MOR the stronger binding of OH to the surface at Ru@Pt than at Pt is expected to increase the activity of the former. These predictions are in agreement with the results of measurements of the catalytic activity of the catalysts, and serve to rationalise the catalytic activity of Ru@Pt with respect to those of Pt for these reactions.

Iridium oxide powders with a surface area of more than 1 m

An important step in the process of producing hydrogen a viable method is to improve the efficiency and reduce the cost of low-temperature water electrolysers. One of the most crucial components is the catalyst used to drive the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Traditionally, the nanosized electrocatalysts are synthesized through a chemical reduction method involving a strong reducing agent like sodium borohydride, polyol, etc. Being able to control the nucleation and growth and therefore the size of the nanocatalysts, however, is not straightforward with the chemical reduction method where the use of surfactants is heavily relied upon, thus complicating the method for the industry. An alternative synthesis route involves the in-situ generation of radicals to serve as reducing agents through high power ultrasound (20 kHz–1 MHz) in a process where water is split into OH- and H-radicals referred to as water sonolysis. This presentation highlights the effects of ultrasonication frequencies, ultrasonication, times, pH solutions, reducing agents, and different saturation gasses on the generation of metallic nanoparticles and their subsequent electrocatalytic activities towards the HER and OER in mild acidic and alkaline environments. A series of physical characterizations on these sonochemically prepared nanoelectrocatalysts will be shown and discussed.

Hydrogen production from anion exchange membrane water electrolysis (AEMWE) is an efficient cost-effective solution to renewable energy storage. Contrary to proton exchange membrane (PEM) electrolysis, AEMWE requires further optimization of its cell design, particularly for the kinetically unfavourable oxygen evolution anode half-cell reaction (OER). In this work we optimize the commercial Fumatech fumion ionomer content in AEMWE anodes using nickel (Ni) nanoparticles (NP) synthesized by chemical reduction. The optimal ionomer content is then applied to Ni-iron (Fe)-based NPs with and without ceria (CeO2), all prepared using the same method. Scanning Electron Microscopy (SEM) of the resulting electrode surfaces, Particle-size Distribution (PSD) of the catalyst inks, and in-situ testing of the monometallic Ni NPs show that the best and most active catalytic layer is obtained using 15 wt% ionomer. AEMWE performance and short-term durability are evaluated in different concentrations of potassium hydroxide (KOH), where the Ni90Fe10 is the best performing Ni-based electrode showing 1.72 V at 0.8 A cm−2 in 1 M KOH after IR-correction, and a degradation rate of 3.3 mV h−1. The addition of ceria to the Ni-based catalysts shows more consistent mass transfer over time likely due to more efficient water transport and bubble release.

The microporous layer (MPL) and the gas diffusion layer (GDL) in a polymer electrolyte membrane (PEM) fuel cell assembly are often treated as separate layers in the literature. However, there exists a considerable third region where the two different materials merge in the coating process. This region has properties that differ from either of the materials that it consists of. Through-plane thermal conductivity and thickness variation under different compaction pressures were measured for such a composite region of two different commercial GDLs, Freudenberg H1410 and Toray Paper TGP-H-030, each treated with a custom-made MPL ink. Thermal conductivity at 15 bar compaction pressure for untreated Freudenberg H1410 GDL is 0.124 ± 0.009 W K-1 m−1 and for the custom-MPL-coated Freudenberg H1410 materials it was increased by the treatment to 0.141 ± 0.004 W K−1 m−1 and 0.145 ± 0.004 W K-1 m−1 for 9.9 wt% and 11.9 wt% ink, respectively. For Toray paper TGP-H-030 the thermal conductivity at 15 bar compaction pressure for GDL only is 0.449 ± 0.009 W K−1 m−1 and for the custom-MPL-coated Toray TGP-H-030 materials it was decreased by the treatment to 0.39 ± 0.05 W K−1 m−1 and 0.39 ± 0.00 W K−1 m−1 for 9.9 wt% and 11.9 wt% ink, respectively. © 2018. This is the authors' accepted and refereed manuscript to the article. The final authenticated version is available online at: http://jes.ecsdl.org/content/165/7/F514

A method for measuring downstream concentration effects through electrochemical impedance spectroscopy at double channel electrodes is demonstrated. An ac current perturbation is applied at an upstream working electrode and the resulting ac potential response at a downstream sensing electrode is measured. This generator-detector scheme is implemented with a single potentiostat. Experimental data for a reversible redox couple are presented and good agreement is found with numerical simulations. A qualitative explanation of the features is given which lays the foundation for a more rigorous theoretical treatment. Relationships with flow rate and frequency are found that can scale the data to lie on a universal curve. This is the authors' manuscript to the article (preprint).

The electrolyte is one of the three essential constituents of a Lithium-Ion battery (LiB) in addition to the anode and cathode. During increasingly high power and high current charging and discharging, the requirement for the electrolyte becomes more strict. Solid State Electrolyte (SSE) sees its niche for high power applications due to its ability to suppress concentration polarization and otherwise stable properties also related to safety. During high power and high current cycling, heat management becomes more important and thermal conductivity measurements are needed. In this work, thermal conductivity was measured for three types of solid state electrolytes: Li 7 La 3 Zr 2 O 12 (LLZO), Li 1 . 5 Al 0 . 5 Ge 1 . 5 (PO 4 ) 3 (LAGP), and Li 1 . 3 Al 0 . 3 Ti 1 . 7 (PO 4 ) 3 (LATP) at different compaction pressures. LAGP and LATP were measured after sintering, and LLZO was measured before and after sintering the sample material. Thermal conductivity for the sintered electrolytes was measured to 0.470 &plusmn, 0.009 WK - 1 m - 1 , 0.5 &plusmn, 0.2 WK - 1 m - 1 and 0.49 &plusmn, 0.02 WK - 1 m - 1 for LLZO, LAGP, and LATP respectively. Before sintering, LLZO showed a thermal conductivity of 0.22 &plusmn, 0.02 WK - 1 m - 1 . An analytical temperature distribution model for a battery stack of 24 cells shows temperature differences between battery center and edge of 1&ndash, 2 K for standard liquid electrolytes and 7&ndash, 9 K for solid state electrolytes, both at the same C-rate of four.

Nickel/Nickel oxide (Ni/NiO) nanosheets heterostructure is a cheap and active catalyst for hydrogen evolution reaction (HER) in alkaline electrolytes. However, the reason for this activity is still under debate. Herein in-situ Raman electrochemistry has been established as a method to probe interfacial intermediates and correlate the performance of various nickel catalysts (Ni, NiO, and Ni/NiO nanosheets) during HER. In-situ Raman spectroscopy demonstrated that Ni/NiO nanosheet heterostructure maintained β-Ni(OH)2 species initially, which may contribute to the superior initial HER activity. Ni/NiO nanosheets lost β-Ni(OH)2 species by preserving a high cathodic overpotential (-0.4 V vs. RHE) for 2000 sec. The results confirmed the importance of Ni metal sites in addition to NiO sites and maintaining hydroxide species for superior and durable HER activity. These results can be utilized to design an efficient and durable catalyst for alkaline electrolyzers for the sustainable production of hydrogen. © 2020 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

Anion exchange membrane water electrolysis (AEMWE) has acquired substantial consideration as a cost-effective hydrogen production technology. The anion ionomer content in the catalyst layers during hydrogen and oxygen evolution reaction (HER and OER) is of ultimate significance. Herein, an in-situ half-cell analysis with reference electrodes was carried out for simultaneous potential measurements and identification of the influence of the anion exchange ionomer (AEI) content on anode and cathode performance. The measured half-cell potentials proved the influence of AEI content on the catalytic activity of HER and OER, which was supported by the rotating disk electrode (RDE) measurements. Cathode overpotential of Ni/C was not negligible and more affected by the AEI content than anode with the optimized AEI content of 10 wt% while NiO anode OER overpotential was independent of the AEI content. For the same AEI content, PGM catalysts showed higher electroactivity than Ni-based catalysts for HER and OER and the cathode catalyst's intrinsic activity is of high importance in the AEM electrolysis operation. Post-mortem analysis by SEM mapping of both AEI and catalyst distributions on the electrode surface showed the effect of AEI loading on the catalyst morphology, which could be related to the electrode performance. ©2020 The Author(s). Published by Elsevier Ltd on behalf of Hydrogen Energy PublicationsLLC. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

This work highlights the fact that the activity of an already active metal/surface, i.e. Ni, can be increased even further by combining it with metals/surfaces that exhibit low activity, i.e. Pt and Al, when used on their own. Combinatorial screening was conducted on plasma vapour deposited PtxNiyAlz thin-film ratios for the oxygen evolution reaction in alkaline medium. All co-deposited thin films were simultaneously evaluated employing a multichannel potentiostat with Pt9Ni56Al35 exhibiting the highest current at 1.39 V (SHE). Subsequent deposition on a glassy carbon insert followed by electrochemical characterization revealed that Pt9Ni56Al35 performed better than its constituent components in that it exhibited an overpotential of 487 mV at 10 mA cm−2 compared to 590 mV, 941 mV, and 1379 mV for the overpotentials of vapour deposited Ni, Pt and Al respectively. Subsequent evaluation of co-deposited Pt9Ni56Al35, as an electrocatalyst on a nickel woven mesh anode inside a membraneless divergent electrode-flow-through (DEFT™) alkaline electrolyser, resulted in a current density of 1198 mA cm−2 at a cell potential of 2 VDC. This represents the highest current density to date for a membraneless alkaline electrolyser.

An on-chip thin-film palladium hydride reference electrode is described for use with microfluidic electrochemical cells. A Pd electrode fabricated by photolithographic methods is charged with hydrogen in-situ with a simple current step technique. The placement of the reference electrode in a side channel means that it is unaffected by species in the main channel. Placement upstream of the working and sense electrodes is shown to be a significant improvement over cells with the reference electrode placed externally. The adverse effects of solution resistance are investigated quantitatively, and it is shown that the described configuration allows for high current experiments while maintaining accurate potential measurement. A simple formula for calculating the maximum current density for a certain cell geometry and electrolyte resistivity is presented. © 2016 Elsevier Ltd. All rights reserved. This is the authors' accepted and refereed manuscript to the article. Author's post-print must be released with a Creative Commons Attribution Non-Commercial No Derivatives License.

Understanding oxidation kinetics and reaction mechanism at elevated temperatures is paramount to making efficient fuel cells that can run at temperatures higher than 100oC. We describe a method that allows for studies of aqueous electrochemistry at temperatures above the normal boiling point of water, and this system is used to study potential fuels for direct fuel fed fuel cells. Two alcohols with very different partial pressures at temperatures above 100oC are used in this study: methanol and glycerol. A self-pressurized glass autoclave heated in an oil bath is used for this purpose, and a model of the autoclave is shown in Fig. 1a. Slow ramping of the temperature allows for efficient data acquisition by using cyclic voltammetry up to 140oC, exemplified by Fig. 1b, and kinetic parameters such as onset potentials, Tafel slopes and activation energies are found and discussed for the relevant fuels. For methanol oxidation, dissociative water adsorption plays a key limiting role in the total reaction of methanol to CO2 at all temperatures. For glycerol oxidation, some partial oxidation products do not require an oxygen donor in the form of adsorbed water for their formation. This is deemed to play a fundamental role giving a large drop in overpotential at temperatures above 110oC, and making glycerol a potential fuel cell candidate at these temperatures. Therefore, a partial oxidation of glycerol in a fuel cell offers a potential method for a combined fuel cell and value-adding process for abundant glycerol. Figure 1

A miniaturised abiotical fuel cell designed for operation inside a physiologically relevant mixed fuel environment of dissolved di-oxygen (DO) and glucose, have been realized by embedding the glucose sensitive anode below a porous oxygen scavenging cathode. Experimental results showed the cell capable of maintaining a power density of 2.33 ± 0.11 μW cm−2 at a current density of 7.7 μA cm−2 and a cell potential of 0.30 ± 0.01 V. This is comparable to a simulated result of 7.9 μA cm−2 in which the DO concentration from the bulk solution of 60 μM (2 ppm) were predicted to have fallen to 35 μM (1.18 ppm) before entering the cell and reacting with the anode. In contrast, the flux of glucose supplied to the anode was found to maintain a concentration of 3.7 mM inside the cell (from a bulk concentration of 5 mM). The generated power was approximately 80% of the recorded peak power density of 2.83 ± 0.24 μW, that was obtained from separating the fuels prior to use. This suggests that the proposed design were able to limit the amount of DO entering the cell prior to catalysis, and thereby minimize any reduction in the overall current density.

Improvements on catalysts for electrochemical energy conversion is highly important if technologies such as fuel cells and electrolyzers are to become economically viable in the future. These improvements typically lie in the optimization of the catalyst’s particle size and available surface area, which means that nucleation and growth conditions during the synthesis must be controlled precisely. Common ways of producing such catalysts today involve chemical reduction methods were reducing agents like NaBH4 or ethylene glycol are used to reduce metal salts to their metallic state [1]. Even though such methods are fast and scalable, few ways are available for careful control over the nucleation and growth of the nanoparticles. To allow for better control over the nucleation and growth of nanoparticles, a sonochemical synthesis method can be employed instead [1]. In sonochemistry, high power ultrasound is applied to an aqueous metal precursor solution resulting in the formation of H-radicals and OH-radicals in the cavitation bubbles [1]. The highly reactive radicals will diffuse into the solution and reduce the metal ions to metallic nanoparticles. The nucleation and growth conditions can therefore simply be manipulated by controlling the rate of radical formation which is directly related to the ultrasound parameters. Several studies have found that the radical formation rate (or the metal reduction rate) is affected by the ultrasound frequency [2][3], ultrasound power [3], solution temperature [3], types of dissolved gasses [3], types of alcohols used [4], and types of surfactants used [5]. The ease of changing these parameters therefore ensures that nanoparticles of optimal sizes can be produced. In this project we have started to investigate exactly how ultrasound parameters influence the radical formation rate in aqueous systems. This information can therefore be used to synthesize electrocatalysts optimized for HER and OER. Initial investigations of how Ni- and Fe -precursors are affected by ultrasound have also been performed. Sonochemical assisted synthesis of NiFe nanoparticles with NaBH4 was also assessed as a potential hybrid solution. The results from the investigations of the ultrasound parameters suggested that the addition of ethanol effectively leads to a scavenging of the primary radicals in the solution. Consequently, more radicals become available for reducing metal ions, and the reduction rate increases. Higher ultrasonic power and lower ultrasonic frequency (580 kHz was the lowest frequency used in the experiment) increase the radical formation, which is supported by previous findings [2][3]. The effect of dissolved gasses showed that O2 saturation gave the highest radical yield. However, this can be traced to the sonolysis of O2 itself which lead to additional radical formation from the dissolved gas, and not just from the water vapor in the cavitation bubbles [3]. The ideal solution temperature was found to be dependent on the type of dissolved gas, with Ar exhibiting a higher ideal temperature than O2. The initial investigations of Ni- and Fe-precursors showed that the sonochemical reduction was not appreciable in the short time frame which was used (30 min). Longer sonication times will be attempted in future works. For the sonochemical assisted synthesis, NaBH4 was added as a reducing agent to aid the reduction, and an ultrasonic bath was used as the ultrasound source (42 kHz). Physical characterization of the resulting particles showed a significant decrease in the particle size due to the application of ultrasound. However, these changes were attributed to the mechanical effects most dominant at lower ultrasonic frequencies. Similar experiments will be attempted at higher frequencies to observe if the chemical effects of ultrasound act similarly. References Bruno G. Pollet. “The use of ultrasound for the fabrication of fuel cell materials”. International Journal of Hydrogen Energy 35.21 (2010). VIII symposium of the Mexican Hydrogen Society, pp. 11986–12004 K Okitsu et al. “Sonochemical synthesis of gold nanoparticles: effects of ultrasound frequency”. The journal of physical chemistry. B109.44 (2005), p. 20673 S Merouani et al. “Sensitivity of free radicals production in acoustically driven bubble to the ultrasonic frequency and nature of dissolved gases”. Ultrasonics – Sonochemistry 22.2 (2015), pp. 41–50 Rachel A Caruso et al. “Sonochemical formation of colloidal platinum”. Colloids and Surfaces A: Physicochemical and Engineering Aspects 169.1-3 (2000), pp. 219–225 K Okitsu et al. “Sonochemical preparation of ultrafine palladium particles”. Chemistry of Materials (USA) 8.2 (1996), pp. 315–317

Transition metal mixed oxides have been considered as promising catalysts for OER in alkaline media due to high catalytic activity, possible long lifetime and cheap alternatives to precious metal oxides [1-3]. Increasing research interest has been dedicated to Ni-based OER catalysts in particular, which possesses all desired qualities for a catalyst including being earth-abundant and have theoretically high catalytic activity [1]. Iron impurities in nickel hydroxide was found to lower OER overpotential in Ni-based alkaline batteries [4, 5], which paved the way for NiFe catalysts as active OER electrocatalysts in water electrolysis [5-9]. Large use of Ni-rich materials is becoming an increasing difficulty in alkaline electrolysis, and the search for cheaper bulk materials has recently been intensified. In particular, cheaper stainless steels being a source of both Fe and Ni have shown promise as OER electrode. However, the as-received stainless steel has low OER activity and some surface treatment, enriching the surface with nickel is necessary. In this work, we activate as-received 316 stainless steel bulk material by electrooxidation at 1.72 V vs RHE in KOH electrolyte at room temperature. We study the effect of electrolyte pH during activation as well as oxidation time. The electrode surface layer is studied using XPS, GDOES and SEM, while the surface activity is studied electrochemically using potential step and linear sweep voltammetry in a three-electrode Teflon cell. The active surface area was assessed using cyclic voltammetry. Reaction order and Tafel slope are determined to specify the reaction mechanism. We show that surface treatment of 316 stainless steel in the highest concentration of KOH (7.5 M) gives the highest activity for a minimum of 240 minutes oxidation time. Longer oxidation times did not improve electrochemical activity. Surface analysis by XPS, SEM and GDOES show a significant increase in surface Ni after activation, which was correlated to the improved activity. The surface content of Ni increased in general with increasing electrolyte pH during activation. SEM indicates small crystals on the surface, which could be due to precipitation of dissolved species on the activated samples. The best pretreatment performed in this study leads to an overvoltage of 320 mV at 10 mA cm-2. Krasil’shchikov reaction pathway is assigned as the OER reaction mechanism corresponding to the measured reaction order and Tafel slope. All the samples have the same Tafel slope. Repetitive polarization curves after 24h chronoamperometry indicate negligible change in performance with time. This indicates that the activated stainless steel is a promising electrode material for oxygen evolution. Han, L., S. Dong, and E. Wang, Transition‐metal (Co, Ni, and Fe)‐based electrocatalysts for the water oxidation reaction. Advanced materials, 2016. 28(42): p. 9266-9291. Singh, R., J. Singh, and A. Singh, Electrocatalytic properties of new spinel-type MMoO4 (M= Fe, Co and Ni) electrodes for oxygen evolution in alkaline solutions. international journal of hydrogen energy, 2008. 33(16): p. 4260-4264. Song, F., et al., Transition metal oxides as electrocatalysts for the oxygen evolution reaction in alkaline solutions: an application-inspired renaissance. Journal of the American Chemical Society, 2018. 140(25): p. 7748-7759. Conway, B. and P. Bourgault, The electrochemical behavior of the nickel–nickel oxide electrode: Part I. Kinetics of self-discharge. Canadian Journal of Chemistry, 1959. 37(1): p. 292-307. Lyons, M.E. and M.P. Brandon, The oxygen evolution reaction on passive oxide covered transition metal electrodes in aqueous alkaline solution. Part 1-Nickel. Int. J. Electrochem. Sci, 2008. 3(12): p. 1386-1424.

Renewable hydrogen generation is a crucial step to reach a sustainable society. Water electrolysis represents a cheap and effective method for hydrogen production. Anion-exchange membranes (AEM) water electrolysis utilizes inexpensive transition metal electrocatalysts, membranes, ionomers, and construction materials.1 , 2 In this work we report characterization of NiMo and NiCoFe catalysts that have been optimized as hydrogen and oxygen evolution reaction (HER and OER) catalysts. The characterization includes studies of ionomer-electrolyte-catalyst interaction as a basis for optimizing HER and OER performance under real operating conditions. With these optimized catalysts in an AEM electrolyzer we have achieved 1 A cm-2 at 1.95 V in 1 M KOH at 50 oC. The AEM electrolyzer was stable for 65 hours at 0.5 A cm-2 in 0.1 M KOH. The catalysts developed here will be significant in supporting the pursuit of cheap hydrogen fuel. References 1 A. Faid, A. Oyarce Barnett, F. Seland, S. Sunde, A. Y. Faid, A. Oyarce Barnett, F. Seland, and S. Sunde, Catalysts, 2018, 8, 614. 2 A. Y. Faid, A. O. Barnett, F. Seland, and S. Sunde, J. Electrochem. Soc., 2019, 166, F519–F533. Figure 1

Anion exchange membrane water electrolysis (AEMWE) is an efficient and cost-effective solution to renewable energy storage due to its compact cell design and potential to operate using non-noble metal catalysts. [1] A known challenge to water electrolysis is the kinetically unfavourable oxygen evolution half-cell reaction (OER). Studies have shown that combining nickel (Ni) with small quantities of iron (Fe) can significantly enhances activity towards OER [2], and it has been shown that adding cerium oxide (CeO2), an oxygen conducting support, to catalyst materials can enhance catalytic processes. [3] AEMWE electrodes typically consist of a catalyst material, an ionomer and a solvent. For an efficient cell design, it is crucial to have an active catalyst, as well as the right amount of ionomer to properly stabilize and bind the catalytic layer, while still allowing for high hydroxide ion transport [4]. As such, this study covers the ionomer content optimization of NiFe-based nanoparticles (NPs) supported on CeO2 for anodes in AEMWE using a catalyst coated surface (CCS) electrode configuration. Preliminary AEMWE testing of the NiFe materials without ink optimization is covered in our previous work [5]. The materials tested were synthesized by chemical reduction in ethanol with sodium borohydride, and in-situ testing was done with a Fumatech membrane and ionomer. The ionomer content was tested on pure Ni NPs and the amounts tested were 7, 15, 25, 35 and 45 wt%. Scanning Electron Microscopy (SEM) of the resulting electrodes, Particle-size Distribution (PSD) of the catalyst inks, and in-situ testing showed that the best and most active catalytic layer was formed with 15 wt% ionomer. With the optimal ionomer content found, a more rigorous evaluation of AEMWE performance was carried out on NixFe(100-x) (x=90, 80 at%) both of which were also tested with 10 wt% CeO2. Polarization curves and electrochemical impedance spectroscopy results in 1 M and 0.1 M KOH are summarized and discussed. Additionally, catalyst stability of each of the materials was characterized by holding 0.5 A cm-2 for 12 hours, while measuring impedance every hour. Future work of this study will include long-term stability testing as well as testing the performance of different commercial and lab produced ionomer-membrane combinations with the Ni-based materials. [1] M. Tahir, L. Pan, F. Idrees, X. Zhang, L. Wang, J. Zou and Z. L. Wang, Nano Energy 2017, 37, 136. [2] M. Gong and H Dai, Nano Research 2015, 8, 23. [3] H. A. E. Dole and E. A. Baranova, ChemCatChem 2016, 8, 1977. [4] G. Li, D. Yang and P. A. Chuang, ACS Catal. 2018, 8, 11688. [5] E. Cossar, A. O. Barnett, F. Seland, E. A. Baranova, Catalysts 2019, 9, 814.

The methanol oxidation reaction (MOR) is studied at temperatures up to 140 °C by a combination of cyclic voltammetry, chronoamperometry, and dynamic electrochemical impedance spectroscopy (dEIS). A mechanistic analysis of the reaction is done based on the Tafel relation, the calculated activation energy, and the fitting of dEIS data. At the fuel cell relevant potentials, 0–0.80 V vs RHE, the MOR mechanism is similar at all temperatures. The rate-determining step is the adsorption of water at low overpotentials (< 0.50 V vs RHE), a combination of the methanol adsorption reaction and the surface reaction between adsorbed CO and OH at intermediate potentials (0.50–0.65 V vs RHE), and the methanol adsorption reaction at high potentials (> 0.65 V vs RHE). The shoulder on the oxidation peak at 0.60–0.65 V vs RHE corresponds well with where the CO coverage approaches zero. © 2018. This is the authors’ accepted and refereed manuscript to the article. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/

Interfacial contact resistance (ICR) is one of the remaining hurdles for successful implementation of stainless steel bipolar plates in PEM fuel cells. We have developed a reliable method, using thin gold wires, to measure the interfacial contact resistance between the bipolar plate material and the porous transport layer during fuel cell operation. The ICR values were found to be in the same range as the ICR values measured ex situ after fuel cell operation. Local ex situ ICR measurements on tested plates indicate uneven current distribution during fuel cell operation. Consequently, an average between three measuring points was used for the in situ measurements, which enabled consistent monitoring of the ICR development alongside fuel cell performance. For almost all of the tests, the largest ICR changes took place within the first two hours of operation, showing the importance of early ICR measurements. Non-coated stainless steel and titanium-coated steel BPPs experienced a higher ICR compared to the gold coated stainless steel. © The Author(s) 2019. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/)

Many renewable electricity sources (e.g., wind and solar) are intermittent, and in many cases peak production does not align with peak consumption. One way to store this excess renewable energy is by means of hydrogen gas through the process of water electrolysis. The stored energy in hydrogen gas can be recovered with a fuel cell when needed. [1] This way fuel cells can be an energy buffer and help to stabilize power systems based on renewable energy sources. A proton exchange membrane fuel cell (PEMFC) consists of several components. The membrane electrode assembly (MEA) is sandwiched between gas diffusion layers (GDLs) on each side. GDLs in fuel cells have to satisfy a range of conflicting demands. They must deliver good mass transport, but also good electrical and thermal transport. In this work the thermal conductivity of two commercial GDLs was measured with either hydrogen, air, or argon present inside their pores. The results show an increase of up to 19% with regard to the thermal conductivity for the Freudenberg H1410 GDL with hydrogen present in the pores as opposed to measurements with air present. The thermal conductivity in the Sigracet 10BA GDL was also enhanced, with an increase of 15% with hydrogen present in the pores. This correlates with the thermal conductivity of hydrogen gas, which is higher than that of air. Furthermore, the results suggest that the GDL materials have a lower thermal conductivity with argon gas present in the pores. The thermal conductivity for Freudenberg H1410 increased from 0.119 ± 0.011 WK-1m-1 for air to a thermal conductivity of 0.140 ± 0.015 WK-1m-1 for hydrogen gas at a compaction pressure of 10 bar. The thermal conductivity of Sigracet 10BA increased from 0.30 ± 0.05 WK-1m-1 for air to a thermal conductivity of 0.32 ± 0.03 WK-1m-1 for hydrogen gas at a compaction pressure of 10 bar. These results suggest that the gas present in the pores has a significant influence on the thermal conductivity of the GDL. Additionally, a 2D thermal model has been constructed to represent the impact of the results on the temperature distribution inside a fuel cell, see figure 1. The considerable temperature gradients inside the single cells need to be considered when assessing lifetime and degradation effects [1-4]. Judging by the scarcity of data on this in the literature this is not the case as of today. Figure 1: PEMFC land temperature profiles saturated with air, argon, or hydrogen on the anode side. The dashed vertical lines represent the border between different materials in the MEA References [1] O. S. Burheim, Engineering Energy Storage, 1st edition, Academic Press, 2017. [2] R. Bock, A.D. Shum, X. Xiao, H. Karoliussen, F. Seland, I.V. Zenyuk and O.S. Burheim, Thermal conductivity and compaction of GDL-MPL interfacial composite material, J. Electrochem. Soc. 2018 165(7): F514-F525 [3] R. Bock, H. Karoliussen, B. G. Pollet, M. Secanell, F. Seland, D. Stanier and O. S. Burheim, The influence of graphitization on the thermal conductivity of catalyst layers and temperature gradients in proton exchange membrane fuel cells, International Journal of Hydrogen Energy, In-press 2018 [4] R. Bock, A. Shum, T. Khoza, F. Seland, N. Hussain, I. V Zenyuk and O. S. Burheim Experimental Study of Thermal Conductivity and Compression Measurements of the GDL-MPL Interfacial Composite Region, ECS Trans. 2016 75(14): 189-199 Figure 1

This work presents an integrated hydrogen production system using reverse electrodialysis (RED) and waste heat, termed Heat to H 2 . The driving potential in RED is a concentration difference over alternating anion and cation exchange membranes, where the electrode potential can be used directly for water splitting at the RED electrodes. Low-grade waste heat is used to restore the concentration difference in RED. In this study we investigate two approaches: one water removal process by evaporation and one salt removal process. Salt is precipitated in the thermally driven salt removal, thus introducing the need for a substantial change in solubility with temperature, which KNO 3 fulfils. Experimental data of ion conductivity of K + and no in ion-exchange membranes is obtained. The ion conductivity of KNO 3 in the membranes was compared to NaCl and found to be equal in cation exchange membranes, but significantly lower in anion exchange membranes. The membrane resistance constitutes 98% of the total ohmic resistance using concentrations relevant for the precipitation process, while for the evaporation process, the membrane resistance constitutes over 70% of the total ohmic resistance at 40 ∘ . The modelled hydrogen production per cross-section area from RED using concentrations relevant for the precipitation process is 0.014 &plusmn, 0.009 m 3 h n a m e d - c o n t e n t c o l o r t y p e r g b c o n t e n t - t y p e b l a c k - 1 (1.1 &plusmn, 0.7 g h n a m e d - c o n t e n t c o l o r t y p e r g b c o n t e n t - t y p e b l a c k - 1 ) at 40 ∘ , while with concentrations relevant for evaporation, the hydrogen production per cross-section area was 0.034 &plusmn, 0.016 m 3 h n a m e d - c o n t e n t c o l o r t y p e r g b c o n t e n t - t y p e b l a c k - 1 (2.6 &plusmn, 1.3 g h n a m e d - c o n t e n t c o l o r t y p e r g b c o n t e n t - t y p e b l a c k - 1 ). The modelled energy needed per cubic meter of hydrogen produced is 55 &plusmn, 22 kWh (700 &plusmn, 300 kWh kg n a m e d - c o n t e n t c o l o r t y p e r g b c o n t e n t - t y p e b l a c k - 1 ) for the evaporation process and 8.22 &plusmn, 0.05 kWh (104.8 &plusmn, 0.6 kWh kg n a m e d - c o n t e n t c o l o r t y p e r g b c o n t e n t - t y p e b l a c k - 1 ) for the precipitation process. Using RED together with the precipitation process has similar energy consumption per volume hydrogen produced compared to