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A peerless inexpensive electrochemical engineering of spherical Pt nanoparticles (nano-Pt: ca. 100 nm in average diameter) was achieved with intersected ferric oxyhydroxide nanotubes (α-FeOOH (goethite): ca. 20 nm in average diameter). The FeOOH@Pt catalyst exhibited ca. 2.5 and 1.94-times increases in the catalytic activity and poisoning tolerance, respectively, of the formic acid electro−oxidation (FAO) – the anodic reaction in the direct formic acid fuel cells (DFAFCs). Surprisingly, with a post-activation of the FeOOH@Pt catalyst at 0.48 V vs. reversible hydrogen electrode (RHE) in 0.2 mol L−1 NaOH, a favorable Fe2+/Fe3+ transformation succeeded to eliminate the permanent CO poisoning of Pt that impaired the catalytic performance of DFAFCs. This was synchronized (relatively to nano-Pt) with a four-fold increase in the catalytic efficiency, ca. −174 mV shift in the onset potential, and eightfold enhancement in the catalyst's durability for FAO. The activated FeOOH@Pt catalyst also showed a mass activity of 296 mA mg−1Pt (at 0.8 V), which was ca. nine times higher than that (34 mA mg−1Pt) of the commercial Pt/C catalyst. The ascertained improvement in the electron transfer at the FeOOH@Pt surface foresees quick industrialization for DFAFCs.

Development of an efficient catalyst for ammonia preparation through electrochemical nitrogen fixation is significant and desirable to relieve the tremendous energy-consumption by the conventional Haber-Bosch process. Herein, the abundant oxygen vacancy-containing CuCeO2@NC composite (denoted as Cu-doped CeO2 nanoparticles supported on carbon nitride) was fabricated by annealing melamine-incorporated metal-organic framework (MOF) of CuCe-BTC (BTC = 1,3,5-benzenetricarboxylic acid) under the reducing atmosphere of 10% H2/Ar. The optimized composite of Cu0·1CeO2@NC achieved a high selectivity and an outstanding electrocatalytic activity with NH3 yield rate of 44.5 μg h−1 mgcat.−1 at −0.5 V versus a reversible hydrogen electrode, surpassing most of the reported electrocatalysts and its analogues without copper and nitrogen atoms as dopants. The favorable performance of Cu0·1CeO2@NC would be ascribed to the synergistic effect of the rich oxygen vacancies and the optimal electrical structure induced by heteroatom doping, further confirmed by X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) spectroscopy, and Raman spectra. Moreover, the great electrochemical selectivity and durability for the longtime electrolysis had been demonstrated. This work offered an insight that the electrocatalytic performance would be regulated by heteroatomic dopants and oxygen vacancy toward MOF-derived materials.

A novel three-dimensional (3D) core-shell nanostructure decorated with plasmonic Au nanoparticles (NPs) was prepared for photoelectrochemical water splitting. In the new nanostructure, ZnO nanorods (NRs) are perpendicular to ZnO nanosheets (NSs), and the ZnO NSs-NRs are coated with a thin TiO2 shell formed by liquid phase deposition. The plasmonic Au NPs were formed in situ on the surface of ZnO NSs-NRs@TiO2 by thermal reduction. A thin TiO2 shell and uniformly distributed Au NPs were successfully obtained. The photoconversion efficiency and photocurrent density of the 3D ZnO NSs-NRs@TiO2-Au nanostructure respectively reached 0.48% and 1.73 mA cm−2 at 1.23 V vs. reversible hydrogen electrode, 4.80 and 4.33 times higher than those of ZnO NSs, respectively. The thin TiO2 shell effectively promoted charge separation, while the surface plasmon resonance effects of the Au NPs improved the photocurrent density. The findings suggest that the 3D ZnO NSs-NRs@TiO2-Au nanostructure is a promising photoanode for photoelectrochemical water splitting.

To design inexpensive carbon catalysts and enhance their oxygen reduction reaction (ORR) activity is critical for developing efficient energy-conversion systems. In this work, a novel Fe-N-C hybrid electrocatalyst with carbon nanolayers-encapsulated Fe3O4 nanoparticles is synthesized successfully by utilizing the molecular-level confinement of graphitic C3N4 structures via hemin biomaterial. Benefiting from the Fe-N structure prevalent on the carbon nanosheets and large mesopore-dominated specific surface area, the synthesized catalyst under optimized conditions shows excellent electrocatalytic performance for ORR with an EORR at 1.08 V versus reversible hydrogen electrode (RHE) and an E1/2 at 0.87 V vs. RHE, and outstanding long-term stability, which is superior to commercial Pt/C catalysts (EORR at 1.04 V versus RHE and E1/2 at 0.84 V versus RHE). Moreover, the low hydrogen peroxide yield (

Hybrid catalysts composed of transition metals and nitrogen-doped carbons have been emerging as one of efficient electrocatalysts for electrochemical CO2-to-CO under ambient conditions. Herein, NiO loaded on mesoporous graphene with tunable concentration of pyridinic nitrogen is rationally synthesized by using low-intensity pulsed laser irradiation and pyrolysis treatments. Comprehensive experiments verify that, it is pyridinic N, rather than pyrrolic N, when bonded to Ni, that significantly enhance the electrochemical CO2 reduction reaction performance. The optimized catalyst exhibits a high CO Faradaic efficiency of 87.5% at a low potential of −0.74 V vs. reversible hydrogen electrode, associated with negligible attenuation of continuous operation over 12 h.

Ammonia (NH3) offers extensive applications in industrial production; moreover, it is a potential carrier for hydrogen energy and an eco-friendly fuel. Electrocatalytic synthesis of NH3 has drawn increasing research attention, wherein an excellent electrocatalyst plays a vital role. Iron (Fe) oxide nanomaterials with their high activity and cost effectiveness of its raw material Fe, have received significant attention in electrocatalytic N2 reduction reaction (NRR) to synthesize NH3. This study reports a rapid and cost-effective electrochemical method for synthesizing magnetic Fe3O4 nanoparticles, achieving gram-level production under ambient conditions. The synthesized magnetic Fe3O4 nanoparticles as electrocatalyst for NRR, achieved excellent faradaic efficiency of 16.9% and an optimal NH3 yield of 12.09 μg h−1 mg−1cat. at −0.15 V (versus the reversible hydrogen electrode (RHE)) in 0.1 M Na2SO4. Besides, density functional theory (DFT) calculations indicate that the N≡N bond was fully activated, and the NRR proceeds mainly along the alternating hydrogenation pathway.

Active and durable oxygen reduction reaction (ORR) catalysts are of utmost importance to realize the commercialization of hydrogen fuel cells and metal-air batteries. Al-substituted MnFe2O4-based ternary oxide and reduced graphene oxide (MAF-RGO) nanocomposite is synthesized using an in-situ co-precipitation followed by a hydrothermal process and verified for ORR electrocatalysis in the alkaline electrolyte (0.1 M KOH). MAF-RGO is first analyzed using physicochemical characterization tools including X-ray diffraction, Raman spectroscopy, sorption studies, electron microscopy, X-ray photoelectron spectroscopy, etc. Further, the characteristic ORR peak centered at 0.56 V vs. reversible hydrogen electrode (RHE) in cyclic voltammetry (CV) studies confirms the electrocatalytic performance of MAF-RGO. The ORR onset potential of 0.92 V vs. RHE is obtained in linear sweep voltammetry (LSV) measurement at 1600 rpm in O2-saturated electrolyte exhibiting an improved ORR performance as compared to the commercial electrocatalyst. The reduction kinetics is observed to follow the desirable near 4-e- mechanism. In addition, the electrocatalyst exhibits improved relative current stability of 86% and methanol poisoning resistance of 82%, which is better in comparison to the standard Pt/C. The observed electrochemical performance results from the synergism between the oxygen vacancy-rich Al-substituted metallic oxide active species and the functional group enriched predominantly mesoporous RGO sheets with excellent electrical conductivity. The introduction of metallic species enhanced the inter-planar spacing between graphitic sheets easing the maneuver of reactant species through the electrocatalyst and accessing more ORR-active sites. This study establishes the potency of mixed transition metal oxide/nanocarbon composites as durable high-performance ORR-active systems.

Electrocatalytic nitrogen fixation under ambient conditions represents an energy-saving sustainable alternative strategy to the energy-consuming traditional Haber–Bosch process toward ammonia synthesis. However, the traditional electrocatalysts for nitrogen reduction reaction (NRR) often suffer low selectivity and low activity. From quantum-mechanical calculations, we obtain a benefit clue that the Ni atom adsorbed by the first hydrogen ion in the catalyst exhibits selectivity for the adsorption of N2 and other H atoms, and it preferentially adsorbs N2 molecules. Thus, we propose an interfacial engineering strategy to simultaneously accelerate selectivity and activity using metal/metal hydroxide. The remarkable activity of metal/metal hydroxide originates from its synergized water dissociation and unique hydrogenation pathway of metal hydride. The priority absorption of the N2 suppresses the competitive hydrogen evolution reaction and accelerates the kinetics to generate ∗N2H: ∗H + N2 → ∗N2H, which a is rate-limiting step for NH3 synthesis. Using Ni/NiFe–OH as prototypes, here we show that selectivity and catalytic activity are simultaneously enhanced, surprisingly, in simple inorganic hybrid and confers exceptionally Faradaic efficiency of 23.34% and NH3 yield 19.74 μg h−1 cm−2 at −0.15 V versus reversible hydrogen electrode (RHE) in 0.5 M KOH electrolyte under ambient conditions. The long-term durability is also excellent. This work provides a possibility for the rational design of efficient electrocatalysts for N2 electrochemical reduction with a large-scale production.

Artificial nitrogen fixation is emerging as a promising approach for synthesis of ammonia at mild conditions. Inspired by biological nitrogen fixation based on bacteria containing iron, zinc doped Fe2O3 nanoparticles are proposed as an efficient and earth abundant electrocatalyst for converting N2 to NH3. In neutral media, it achieves a maximum Faradaic efficiency (FE) of 10.4% and a large NH3 yield rate of 15.1 μg h−1 mg−1cat. at −0.5 V vs. reversible hydrogen electrode. This catalyst also exhibits excellent selectivity and stability. Theoretical calculations suggest the reaction follows the associative enzymatic mechanism and it has a barrier of as low as 0.68 eV.

The electrochemical conversion of N2 to NH3 is an interesting research topic as it provided an alternative and energy-saving method compared with the traditional way of NH3 production. Although different materials have been proposed for N2 reduction, the use of defects in oxides was only reported recently and the relevant working mechanism was not fully revealed. In this study, Sr was used as the dopant for LaFeO3 to create oxygen vacancies, forming the Sr-doped LFO (La0.5Sr0.5FeO3-δ) perovskite oxide. The La0.5Sr0.5FeO3-δ ceramic oxide used as a catalyst achieves an NH3 yield of 11.51 μgh−1 mg−1 and the desirable faradic efficiency (F.E.) of 0.54% at −0.6 V vs reversible hydrogen electrode (RHE), which surpassed that of LaFeO3 nanoparticles. The 15N isotope labeling method was employed to prove the La0.5Sr0.5FeO3-δ catalyst had the function of converting N2 into NH3 under the electrolysis condition. The first principle calculations were used to investigate the mechanism at the atomistic level, revealing that the free energy barriers changed significantly with the introduction of oxygen vacancies that accelerated the overall nitrogen reduction reaction (NRR) procedure.

Atomically dispersed transition metals anchored on N-doped carbon have been successfully developed as promising electrocatalysts for acidic oxygen reduction reaction (ORR). Nonetheless, how to introduce and construct single-atomic active sites is still a big challenge. Herein, a novel concave dodecahedron catalyst of N-doped carbon (FeCuNC) with well confined atomically dispersed bivalent Fe sites was facilely developed via a Cu-assisted induced strategy. The obtained catalyst delivered outstanding ORR performance in 0.5 M H2SO4 media with a half-wave potential (E1/2) of 0.82 V (vs reversible hydrogen electrode, RHE), stemming from the highly active bivalent Fe-Nx sites with sufficient exposure and accessibility guaranteed by the high specific surface area and curved surface. This work provides a simple but efficient metal-assisted induced strategy to tune the configurations of atomically dispersed active sites as well as microscopy structures of carbon matrix to develop promising PGM-free catalysts for proton exchange membrane fuel cell (PEMFC) applications.

A class of non-precious metal and highly efficient catalysts (Fe–N(PIL)/C) for the oxygen reduction reaction (ORR)were prepared by a two-step reaction involving polymerization and one-pot high-temperature pyrolysis reaction. The characteristics of Fe–N(PIL)/C electrocatalyst samples were investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS). Additionally, the electrocatalytic properties were tested by linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). Under alkaline conditions, the Fe–N(PIL)/C catalyst exhibited a 2D-mesoporous structure with prominent catalytic activity. The Eon and E1/2 reached 1.08 V and 0.93 V (vs. a reversible hydrogen electrode), respectively. The catalyst showed excellent ORR catalytic performance and stability and is superior to a 20 wt% Pt/C catalyst. This could be attributed to its mesoporous structure and the high content of Fe–N activity sites that enable it to carry out a nearly 4e− reaction pathway for the ORR.

Developing high performance, good stability and noble-metal-free electrocatalysts for renewable hydrogen evolution reaction (HER) remain a substantial challenge. Herein, we introduce a novel facile one-step in-situ strategy through pyrolysis for the synthesis of Co2P nanoparticles encapsulated Boron, Nitrogen, and Phosphorous tri-doped carbon nanotubes (Co2P/BNP-CNTs). The synergetic effect between Co2P nanoparticles and heteroatom doped CNTs contributes to the remarkable HER performance. The Co2P/BNP-CNT-900 electrocatalyst shows a low overpotential of 133 mV at a current density of 10 mA cm−2 and a small Tafel slope of 90 mV dec−1 in 0.1 M KOH media. More importantly, the Co2P/BNP-CNT-900 electrocatalyst exhibits superior long-term stability in alkaline solution at −0.25 V versus Reversible Hydrogen Electrode (RHE) for 15 h and up to 1000 cycles with negligible performance loss. Overall, our works suggest a one-pot facile synthesis strategy for rational designing high-performance electrocatalysts with enhanced HER performance.

Tin dioxide (SnO2) nanoflakes electrodes were developed by a simple hydrothermal synthesis with a length of ~1.5 μm. Based on this electrode, g-C3N4 layer with an energetic band gap of about 2.7 eV was deposited by electrophoretic deposition under constant potential (30 V) for 3, 5 and 10 min, respectively. To enhance the chemical adsorption of g-C3N4 sheets on SnO2 nanoflake film, the SnO2 film was put in 0.5 M NaOH solution, and OH− ions were coated via the entire surface area of SnO2 film. As increasing the deposited time of the g-C3N4 layer to 5 min, the g-C3N4 nanosheets steadily covered the surface area. In particular, g-C3N4 (5min)/SnO2 nanoflake film exhibited the maximum photocurrent density (JSC), 0.15 mA/cm2 at 1.23 V vs. Reversible Hydrogen Electrode under the full sun, and a slight photoresponse in the visible light of 400–450 nm contributes to the enhancement of JSC, compared to that of SnO2 nanoflake film. Furthermore, the interfacial resistance after the coating of g-C3N4 layer is sharply reduced, which is resulted from the electrocatalytic effect of g-C3N4 layer. Thus, the heterojunction developed between the core SnO2 layer showing a high conductivity and the shell g-C3N4 layer as the visible light absorbing medium can improve the photoelectrochemical performance.

In this paper, we present a solvothermal synthesis of iron phosphide electrocatalysts using a triphenylphosphine (TPP) precursor. The synthetic protocol generates Fe2P phase at 300 °C and FeP phase at 350 °C. To enhance the catalytic activities of obtained iron phosphide particles heat-treatments were carried out at elevated temperatures. Annealing at 500 °C under reductive atmosphere induced structural changes in the samples: (i) Fe2P provided a pure Fe3P phase (Fe3P−500 °C) and (ii) FeP transformed into a mixture of iron phosphide phases (Fe2P/FeP−500 °C). Pure Fe2P films was prepared under argon atmosphere at 450 °C (Fe2P−450 °C). The electrocatalytic activities of heat-treated Fe2P−450 °C, Fe3P−500 °C, and Fe2P/FeP−500 °C catalysts were studied for hydrogen evolution reaction (HER) in 0.5 M H2SO4. The HER activities of the iron phosphide catalyst were found to be phase dependent. The lowest electrode potential of 110 mV vs. a reversible hydrogen electrode (RHE) at 10 mA cm−2 was achieved with Fe2P/FeP−500 °C catalyst.

Ammonia synthesis via the electrochemical method is an environmentally-friendly alternative to the Haber-Bosch process. In this work, carbon materials made from fresh cigarette filters were used as the working electrode for the electrochemical synthesis of ammonia. TiO2 was found to exist in the hydrochar of cigarette filters with a mass loading of 0.8 wt%, and showed positive impact on the catalytic performance of the hydrochar. A decent NH3 yield of 6.02 μg mgcat.−1 h−1 and a FE of 8.96% were achieved at −0.1 V versus reversible hydrogen electrode (RHE) in N2-saturated 0.05 M H2SO4. The design of experiments proved that TiO2, which was contained in the hydrochar, indeed played a great role in the catalytic reaction of ammonia synthesis.

Ammonia synthesis based on electrocatalytic nitrogen reduction reaction (NRR) by using renewable sources of energy under ambient conditions has attracted wide research attentions. Herein, we report that the noble-metal-free CuCo2S4/multiwalled carbon nanotube nanocomposite, which is synthesized via a facile one-step hydrothermal and sulfuration approach, can work as the high active and durable catalyst for electrocatalytic NRR. This nanocomposite achieves a high NH3 yield of 137.5 μg h−1 mgcat−1 and a high Faradaic efficiency of 8.7% at −0.5 V vs reversible hydrogen electrode (RHE) in 0.1 M Na2SO4 solution, which outperforms CuCo2S4 counterpart and most reported NRR catalysts. These results reveal that the MWCNT in nanocomposite not only suppresses the aggregation of CuCo2S4 nanoparticles and maximizes the exposure of active sites, but also contributes to the synergistic effect between CuCo2S4 nanoparticles and MWCNT, and facilitates the interfacial reaction kinetics.

We report, the fabrication of molybdenum disulphide (MoS2) wrapped silicon nanowires (Si NWs) for visible light driven water splitting applications. The morphological and elemental studies ensure the vertical alignment of Si NWs wrapped with 2D layered MoS2. The photoelectrocatalytic (PEC) results evidence the significant enhancement in performance of MoS2/Si NWs based hybrid photocathode with ~300 mV (under reversible hydrogen electrode (RHE)) anodic shift in onset potential as that of pristine Si NWs (+0.194 V vs. RHE), and the current density of −26.5 mA/cm2 was achieved at the applied bias of 0 V vs. RHE. Further, the electrochemical impedance studies ensure the interface resistance-free charge transfer between Si NWs and electrolyte via 2D MoS2 layer which provokes rapid hydrogen production. The wrapping of Si NWs with MoS2 protects the superlative photocathode from harsh acid electrolyte environment. The overgrown MoS2 triangular particles with active sulphur edge sites are found to eventually augment the solar hydrogen evolution rate. Further, the PEC performance of our MoS2/Si NWs is also comparable with stable Pt/Si NWs photoelectrode. It is note-worthy that, MoS2/Si NWs hybrid heterostructure would be a potential candidate in future large scale, low cost and day-to-day solar water splitting applications.

CdS has been widely used to modify TiO2-based photoanodes for photoelectrochemical (PEC) water splitting. Due to the poor interface contact between chalcogenides and oxides, however, such CdS modified TiO2 materials usually exhibit inefficient separation and transport of charges, leading to an unsatisfactory efficiency during the PEC water splitting process. Addressing this issue, we herein report a CdS/TiO2 nanotube array (CdS/TNA) photoanode that was fabricated through a successive ion layer absorption and reaction (SILAR) method with an additional subsequent annealing. This post-annealing process is essential to enhance the interface contact between the CdS and the TNAs, resulting in an accelerated transfer of photogenerated electrons from the CdS to the TNAs. In addition, the post-annealing also improves the light absorption capability of the CdS/TNA photoanode. The simultaneous enhancement of charge transport and light absorption provided by the post-annealing is essential for improving the PEC performance of the CdS/TNA photoanode. The CdS/TNA photoanode obtained by this strategy exhibits a much enhanced PEC performance in water splitting, and its photocurrent density and solar-to-hydrogen conversion efficiency could reach 4.56 mA cm−2 at 1.23 V vs. reversible hydrogen electrode and 5.61%, respectively. This simple but effective route can provide a general strategy for obtaining high-performance oxide-based photoelectrodes.

Spinel-type nickel cobaltite with numerous oxygen vacancies is successfully synthesized by hydrothermal and thermal reduction using hydrogen. The effects of oxygen vacancies on the electrochemical activity and stability for the oxygen reduction reaction are investigated. The prepared catalyst displays significantly enhanced oxygen reduction reaction (ORR) catalytic performance under alkaline conditions, which is comparable to that of commercial Pt/C. The oxygen-deficient NiCo2O4 exhibits a very high limiting current density of −5.44 mA cm−2 with onset and half-wave potentials of 0.93 and 0.78 V versus the reversible hydrogen electrode (RHE), respectively. Additionally, it shows excellent durability and resistance to methanol. The enhanced ORR activity and stability of the catalyst can be ascribed to the synergistic effects of the relatively large electrochemical surface area, more exposed active sites, and good electrical conductivity derived from abundant oxygen vacancies.

Photoelectrochemical water splitting using solar energy is a highly promising technology to produce hydrogen as an environmentally friendly and renewable fuel with high-energy density. This approach requires the development of appropriate photoelectrode materials and substrates, which are low-cost and applicable for the fabrication of large area electrodes. In this work, hematite photoelectrodes are grown by aerosol assisted chemical vapour deposition (AA-CVD) onto highly-conductive and bulk porous SnO2 (Sb-doped) ceramic substrates. For such photoelectrodes, the photocurrent density of 2.8 mA cm-2 is achieved in aqueous 0.1 M NaOH under blue LED illumination (λ = 455 nm; 198 mW cm-2) at 1.23 V vs. RHE (reversible hydrogen electrode). This relatively good photoelectrochemical performance of the photoelectrode is achieved despite the simple fabrication process. Good performance is suggested to be related to the three-dimensional morphology of the porous ceramic substrate resulting in excellent light-driven charge carrier harvesting. The porosity of the ceramic substrate allows growth of the photoactive layer (SnO2-grains covered by hematite) to a depth of some micrometers, whereas the thickness of Fe2O3-coating on individual grains is only about 100–150 nm. This architecture of the photoactive layer assures a good light absorption and it creates favourable conditions for charge separation and transport.

This paper reports on a new strategy using a combination of graphene protective layer and amorphous molybdenum sulfide (MoSx) H2-evolving catalyst layer to form a hybrid coating layer that enhances both photocatalytic activity and stability of the p-Cu2O photocathode for the solar H2 generation in water. Graphene sheet was transferred from a copper substrate onto the p-Cu2O electrode surface by a simple solution process, resulting in the creation of p-Cu2O/Gr. A layer of MoSx was deposited further to generate a hybrid p-Cu2O/Gr/MoSx photocathode. In a pH 7 phosphate buffer electrolyte and under 1 Sun light illumination, at the applied potential of 0 V vs. reversible hydrogen electrode (RHE), the resultant p-Cu2O/Gr and p-Cu2O/Gr/MoSx show 7-fold superior catalytic activity and significant enhancement of the stability compared to a pristine p-Cu2O photocathode. The obtained results demonstrate that the p-Cu2O/Gr and p-Cu2O/Gr/MoSx photocathodes are very promising for photoelectrochemical cell water splitting.

While searching for an efficient, non-noble, earth-abundant catalyst for the hydrogen evolution reaction (HER), we synthesized hexagonal dinickel phosphide with different nanostructures using solvothermal phosphidation. Coupled atop p-type Si, this catalyst performed as a p-n heterojunction photocathode assembly and the performance varied when under different electrolyte media. Apart from changing the surface morphology, Ni2P was crystallized with an increase in the Niδ+/Ni2+ ratio as the phosphidation temperature gradually increased. A systematic evaluation of the water splitting reaction shows that a very small amount of catalyst (>85% transmittance for the catalyst layer) exhibits a photocurrent of −10 mA cm−2 with a positive applied potential of 0.05 V versus reversible hydrogen electrode under simulated solar irradiation of AM 1.5G. We discuss the substantial charge transfer process at the depletion layer of the electrode/catalyst and the catalyst/electrolyte interface. Mott–Shottky analysis showed a shift in the flat band potential for Ni2P, which reveals the underlying mechanism for the role of the p-n junction for enhanced photoelectrochemical cell performance.

p-type Cu2O (p-Cu2O) is a promising candidate for engineering of photocathodes for solar H2 generation but it suffers from the photo-induced corrosion process. In this work, we report on the two new strategies to overcome the photo-induced corrosion and to enhance the photocatalytic activity of the p-Cu2O photocathode: (i) a 60-to-300-nm-thick Au layer prepared by sputtering was used as a protective layer to the p-Cu2O electrode; (ii) a thin layer of n-type Cu2O was deposited onto the p-Cu2O electrode surface before sputtering the Au protective layer. For the latter, as a direct result, a pn-Cu2O homojunction was formed that was then protected by the Au thin layer. The pn-Cu2O homojunction helps to enhance the charge separation within the Cu2O electrode, consequently contributes to the enhancement of the photocatalytic activity. Under the standard 1 Sun irradiation, the best Au-protected pn-Cu2O photocathode showed an onset photovoltage of +0.55 V vs. Reversible Hydrogen Electrode (RHE), and a photocurrent density of 0.76 mA/cm2 at an applied potential of 0 V vs. RHE that remained more than 50% after 3 min of operation. Whereas, the bare p-Cu2O showed a photocurrent density of 0.3 mA/cm2 that was completely degraded after 1 min of operation under the identical conditions.

Metallic (1T)-transition metal dichalcogenides is of excellent optical and electrical properties and so especially suitable for various applications including hydrogen evolution catalysis, electronics, and photoelectrons. To date, achieving 1T-MoS2 nanosheets with a simple chemical process still is a challenge. Here we report a hydrothermal synthesis of the 1T-MoS2 nanosheets by incorporating reduced graphene oxide (RGO) or using citric acid/slow successive heating. A small amount of RGO induced the formation of pure 1T-MoS2 nanosheets. Citric acid/slow successive heating induced the formation of 1T-MoS2 nanosheets with a small amount of 2H MoS2. Citric acid/slow successive heating also resulted in smaller average particle size in the present of RGO. Synthesized 1T-MoS2 nanosheets and RGO/1T-MoS2 nanosheet hybrids showed remarkably enhanced conduction and wettability compared with their semiconductor (2H)-nanostructures. Thus, dramatically enhanced hydrogen evolution catalytic activity and stability compared with the 2H-nanostructures were observed. RGO/1T-MoS2 nanosheet hybrids synthesized by incorporating graphene oxide and using citric acid/slow successive heating exhibited greatest photocatalytic activity (71.2 mmol./g·h) and electrocatalytic activity (onset potential of −15 mV vs. reversible hydrogen electrode and Tafel slopes of 43 mV/decade). These facile processes might also be significant for the synthesis and application of other 1T-transition metal dichalcogenides nanosheets and their hybrids with RGO.

Nanocatalysts that boost the sluggish kinetics of oxygen reduction reaction with a long-term durability are crucial for widespread use of low-temperature fuel cells. Here we report a nanoporous intermetallic compound typically composed of platinum–cobalt–aluminum intermetallic core with in-situ grown atomic-layer-thick Pt skin as a novel oxygen-reduction-reaction nanocatalyst with remarkably enhanced performance. Both Pt and Co atoms thermodynamically prefer to locate nearby Al element within face-centered cubic Pt3Al matrix via the formation of strong Pt Al and Co Al bonds, which not only enable synergistic ligand and compressive strain effects to moderately weaken the oxygen adsorption energy of Pt skin, but alleviate the evolution of surface Pt atoms to protect against the further dissolution of less-noble Co and Al. As a result, the nanoporous platinum–cobalt–aluminum nanocatalyst exhibits specific activity of 3.40 mA cm−2Pt and mass activity of 2.2 A mg−1Pt for the oxygen reduction reaction at 0.9 V versus reversible hydrogen electrode (∼13- and ∼20-fold enhancement relative to commercially available platinum nanoparticles supported carbon) with an exceptional durability, showing genuine potential as cathode catalyst in next-generation electrochemical energy conversion devices.

In this work, we developed novel titanium oxynitride (TiOxNy) nanoparticles with diameter of 25 ± 2 nm and crystalline size of ∼15 nm on hydrothermally grown one-dimensional (1D) TiO2 nanorod (TNR) arrays. Herein, the TiOxNy nanoparticles were synthesized by facile nitridation using TiO2 powder at 100% NH3 gas atmosphere. Titanium oxynitride composed of potentially energetic metal-nitrogen bonds (Ti N), compared to the weaker Ti O bond, becomes chemically stable in the alkaline environment, and is considered as a suitable material for photoelectrochemical (PEC) system. The PEC performance of TiOxNy decorated TNR (abbreviated as TiOxNy @TNR) films was evaluated in 0.1 M KOH solution under solar illumination condition, and achieved the potentially high photocurrent density (J) of 2.1 mA/cm2 at 1.23 V versus reversible hydrogen electrode (RHE) (abbreviated as VRHE) in the TiOxNy@TNR arrays, in comparison with the poor photoresponse (0.7 mA/cm2 at 1.23 VRHE) of the pristine TNR arrays. A nearly three-fold enhancement was attained in the TiOxNy decorated TNR arrays, attributed to the high visible light absorption and fast carrier separation, due to the hybridization with the visible active TiOxNy nanoparticles in the cascading band alignment between the TiOxNy and TNR materials. Furthermore, the introduction of TiOxNy layer on the TNR surface quite reduces the interfacial resistance in the solid-liquid interface region, and further, the TiOxNy layer contributes to the passivation of the surface states (e.g., defect, trap sites etc.) where the charge recombination reaction frequently happens, leading to the improvement of PEC performance.

High-performance non-precious metal-doped carbon catalysts for oxygen reduction reactions (ORR) are viable candidates in lieu of platinum-based catalysts. It has been universally reported that active Co–N sites combined with Fe–N sites embedded in carbon matrix represent the most promising active sites for ORR process. Benefiting from the cage-encapsulated-precursor pyrolysis strategy, herein, we fabricated a Fe–N and Co–N homogeneously doped carbon framework by one step. TEM demonstrated the ultimate product had well-defined morphology with Fe (0.54 at%), Co (0.31 at%) and N (2.94 at%) uniformly distributed into the carbon skeleton. The N2 absorption-desorption isotherms indicated the MOF-derived catalyst had a high specific surface area of 647.6 m2 g−1 and inherit hierarchical porosity. Significantly, such FeCo–NC catalyst outperformed a current density (5.6 mA cm−2) at 0.70 V (vs reversible hydrogen electrode) 1.18 times higher than that of a commercial 20 wt% Pt/C (5 mA cm−2) catalyst in alkaline medium, and more positive peak potential of 0.63 V than its counterparts. Its high cycling stability and immunity towards methanol crossover in a wide range pH value showed good potential to be used as cathodes in proton exchange membrane fuel cells (PEMFCs) for long term operation. This simple synthesis strategy would to some degree leverage a cage-encapsulated-precursor for tailored utility of active sites for ORR in a porous carbon framework.

Exploration of multifunctional non-precious metal catalysts towards oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is very important for many clean energy technologies. Here, two trifunctional catalysts based on M (Co, Ni), N and S tridoped carbon nanoplates (Co/N/S-CNPs and Ni/N/S-CNPs) are reported. Due to the relatively higher catalytic site content, graphitization degree and smaller charge-transfer resistance, the Co/N/S-CNPs catalyst shows higher activity and stability for ORR (onset potential of 0.99 V and half-wave potential of 0.87 V vs. RHE (reversible hydrogen electrode)), OER (overpotential at 10 mA cm−2 of 0.37 V) and HER than the Ni/N/S-CNPs catalyst. Furthermore, when constructed with the Co/N/S-CNPs and commercial 20 wt% Pt/C + Ir/C cathodes, respectively, Zn-air battery (ZnAB) based on the Co/N/S-CNPs cathode displays better performance, including a higher power density of 96.0 mW cm−2 and cycling stability at 5 mA cm−2. In addition, an alkaline electrolyzer assembled with the Co/N/S-CNPs catalyst as a bifunctional catalyst can reach 10 mA cm−2 at 1.65 V for overall water splitting and maintain excellent stability even after cycling for 12 h. The present work proves the potential of the Co/N/S-CNPs catalyst for many clean energy devices.

We investigated the hydrogen evolution reaction (HER) properties of multi-wall carbon nanotubes (MWCNTs) treated at extremely high temperature (2600 °C). The heat treatment not only improves the crystallinity of the MWCNTs, but also reduces the carbon-oxygen (C O) bonding as it is replaced by the defect-carbon (sp3 and C H) bonding. These modifications in the heat treated MWCNT structure lead to the increase of electrochemical charge transfer. The heat treatment of MWCNTs in the composite with Pt (MWCNT-Pt composite) further facilitates electrocatalysis. The MWCNTs-Pt composite shows strong enhancement in the HER performance with an onset of overpotential of −0.04 V vs reversible hydrogen electrode and a Tafel slope of 10.9 mV/decade. This performance is indeed better than that of Pt, which is the best working material for HER.

Metal-free electrocatalysts for the oxygen reduction reaction (ORR) were synthesized from cassava residues through a thermal functionalization with sulfuric acid. Their electrocatalytic activities were tested through the ORR performance in basic media. Chemical composition in samples seems to play an important role in their electroactivity, more than textural properties, as the sulfur-treated high-temperature sample (Sy800) has the best performance with an onset potential of 0.69 V vs RHE (reversible hydrogen electrode) and a current of −2.32 mA cm−2 at 0.3 V vs RHE. These functionalized cassava residues are promising materials to be used like carbon-based metal-free electrocatalysts.

Ge doped α-Fe 2 O 3 nanowires are synthesized through a hydrothermal procedure with GeO 2 as a precursor and investigated as photoanodes for water splitting. The content of Ge in the photoanode rises with the increase of the amount of GeO 2 in the precursor solution. A proper amount of Ge facilities the preferred oriented growth of the (110) plane of α-Fe 2 O 3 , while excessive Ge hinders the growth of α-Fe 2 O 3 crystals. The doping of Ge increases the absorption efficiency and decreases the recombining rate of the photogenerated electrons and holes. Ge also improves the density and transfer rate of the charge carriers in the photoanode. Ge doped α-Fe 2 O 3 photoanode exhibits a highest photocurrent density of 0.92 mA cm −2 at 1.23 V vs. reversible hydrogen electrode under AM 1.5 G simulated sunlight, which is nearly twice of that obtained by pure α-Fe 2 O 3 under the same condition.

Amorphous molybdenum sulfide (MoSx) is a promising catalyst for electrochemically producing hydrogen owing to its low cost, excellent catalytic activity, outstanding stability and ease of synthesis, however, the poor electrical conductivity restricts its hydrogen evolution activity. Herein, vertically standing Ti@MoSx core-shell nanowire arrays (TMNs) are synthetized by an electrochemically assistant method. Then, the electrochemical properties of the TMNs in hydrogen evolution reaction are investigated, and the TMNs exhibit enhanced electrochemical properties. The onset overpotential is around 105 mV vs. reversible hydrogen electrode (RHE). The overpotential is 200 mV vs. RHE at 100 mA cm−2, the Tafel slope is 76 mV decade−1. We suggest the remarkable performances of the TMNs for HER can be attributed to the excellent conductivity supplied by the core-shell structure, the affluent mass transport channels provided by the array construction and the highly catalytic activity of S2−/S22− edge sites.

Although sustainable hydrogen production from solar energy is a promising route for the future, the cost of the necessary photovoltaic and photoelectrochemical devices as well as a lack of detailed understanding and control of catalyst interfaces in nanomaterials with high catalytic activity are the largest impediments to commercial implementation. Here, we report how a higher catalytic efficiency can be achieved by utilizing an earth-abundant Nickel oxide (NiO) catalyst via an improved control of the crystalline growth orientation and self-assembly. The relationship between the surface charge and the morphology of the nano-catalysts is investigated using a hydrothermal method where the pH is utilized to control both the crystal growth direction and crystallization of Ni(OH)2 and eventually in NiO, where the self-assembly properties of nanoflakes (NFs) into hierarchical flower-like nickel oxide NFs depend on balancing of forces during synthesis. The surface charge of the NiO at different pH values was measured with electrophoretic dynamic light scattering (EDLS) and is known to be closely related to that of Ni(OH)2 and is here utilized to control the relative change in the surface charge in the precursor solution. By preparing NiO NFs under variation of the pH conditions of the precursor Ni(OH)2 system, the surface energies of exposed lattice planes of the growing nanostructures can be altered and an enhanced crystal growth orientation in a different direction can be controlled. Specifically, the [111] and [220] growth orientation in cubic NiO can be favored or suppressed with respect to the [200] direction. Benefiting from the large surface area provided by the mesoporous NiO NFs, the catalyst electrode exhibits high activity toward the oxygen evolution reactions in alkaline electrolyte. The NiO nanostructure synthesized at pH 10 displays oxygen evolution reaction (OER) overpotential of 0.29 V and 0.35 V versus the reversible hydrogen electrode (RHE) at 1 mA cm−2 and 10 mA cm−2 current density, respectively. This is compared to commercial NiO with more than 0.15 V additional overpotential and the same or lower overpotential compared to RuO2 and IrO2 at alkaline conditions. The results show that the OER catalytic activity can be drastically increased by a detailed control of the crystal growth orientation and the self-assembly behavior where the active surface charge around the point of zero charge during synthesis of the metal hydroxides/oxides is introduced as an important design principle for producing efficient electrocatalysts.

It is important to metal deposition on the electrode surface to increase the electrocatalytic activity of the electrodes. CoWZn coated the graphite rod was used to prepare the cathode electrode. Moreover, then Pt and Ru metals were deposited on the electrode surface. These electrodes were named as CoWZnPt and CoWZnRu. Cyclic voltammetry, electrochemical impedance spectroscopy, and potentiodynamic polarization techniques were used for characterization of electrodes in alkaline media. Hydrogen evolution efficiency was determined by accumulated of hydrogen gas. The catalytic activity for hydrogen evolution reaction of CoWZn, CoWZnPt, and CoWZnRu electrodes was compared. It was reported that modification of the CoWZn electrode with low amounts of Ru enhances the HER activity of the electrodes. The enhancement in the hydrogen evolution activity of the electrodes was attributed to the increase in their real surface area and/or a possible synergistic effect between Co, W, Zn and Ru as well as the well-known intrinsic catalytic activity of Ru. © 2017 Hydrogen Energy Publications LLC

This study investigated the use of synthesized nanozeolite Y to prepare modified carbon paste electrode for electrocatalytic oxidation of hydrogen peroxide. In order to prepare the modified electrodes, the nickel ions were doped to Y zeolite framework through ion exchange mechanism and the electrochemical behaviour of the proposed modified electrode was studied using the cyclic voltammetry technique. The obtained results revealed that modified carbon paste electrode in the form of Ni/NiYCPE is the best electrode for the oxidation of hydrogen peroxide in the alkaline media. The hydrogen peroxide transfer coefficient (α) and the current density were calculated as 0.54 and 6.7 mA/cm 2 , respectively. The catalytic rate constant (K) for this electrocatalytic reaction was calculated through the chronoamperometric technique (K = 0.43 × 10 4 cm 2 s −1 mol −1 ).

There is growing interest in the research of electrocatalysts for oxygen reduction reaction (ORR), which is the key issue for the commercialization of zinc-air (Zn-air) battery. Except precious metal based electrocatalysts, heteroatom-doped carbon materials, as one promising catalyst, also show excellent catalytic activity for ORR. In this work, cobalt phosphide (Co 2 P) and nitrogen, fluorine and phosphorus co-doped mesoporous carbon is synthesized in one step by a phosphorus-containing ionic liquids assisted route. Owing to the synergy effect of Co 2 P and functionalized mesoporous carbon, the catalyst exhibits a high half-wave potential of 0.86 V (vs reversible hydrogen electrode) which is about 30 mV positive than commercial Pt/C, coupled with outstanding stability. At last, the discharge potential of the primary zinc-air battery based on this catalyst is 1.1 V at a constant current density of 50 mA cm −2 (150 mV higher than Pt/C electrode) while the capacity is about 800 mAh g −1 Zn . At the same time, the superior power density is also realized for the zinc-air battery using this catalyst (180 mW cm −2 ).

Here we develop photoanodes based on hierarchical zinc oxide (ZnO) nanostructures such as vertically aligned nanorods (NR), nanorods interconnected by thin nanosheets (NR@TN) and nanorods interconnected by dense nanosheets (NR@DN). The morphological variations were successfully controlled by secondary growth time and the plausible formation mechanisms of these hierarchical ZnO architectures were explained based on the experiment analysis. Under simulated light illumination (AM 1.5, 100 mW cm−2), NR@TN produced a photocurrent density of 0.62 mA/cm2 at 1.23 V vs. reversible hydrogen electrode (vs. RHE). Importantly, 35% enrichment in photoconversion efficiency was observed for NR@TN at much lower bias potential (0.77 V vs. RHE) compared with NR (0.135%) and NR@DN (0.13% at 0.82 V vs. RHE). Key to the improved performance is believed to be synergetic effects of excellent light-trapping characteristics and the large surface-to-volume ratios due to the nanosheet structures. The nanorod connected with thin nanosheet structures improved the efficiency by means of improved charge transfer across the nanostructure/electrolyte interfaces, and efficient charge transport within the material. We believe that the hierarchical ZnO structures can be used in conjunction with doping and/or sensitization to promote the photoelectrochemical (PEC) performance. Further, the ZnO nanorod interconnected with nanosheets morphology presented in this article is extendable to other metal oxide semiconductors to establish a universal protocol for the development of high performance photoanodes in the field of PEC water splitting.

Ceramic composite electrodes comprising an electron-conducting ceramic (Sr-doped LaVO 3 ), a protonic ceramic [Cu and Y-doped Ba(Ce,Zr)O 3 ], and small amounts of CeO 2 and Pd as catalysts were fabricated using an infiltration method for use in an electrochemical hydrogen pump and the hydrogen fluxes and the faradaic efficiency were measured by analyzing the gas compositions. This composite electrode performed well; the area-specific resistance of the electrode polarization at 1 A cm −2 was just 0.15 Ω cm 2 at 973 K in hydrogen pumping mode, and the overpotential at a large current density of 2 A cm −2 was only about 1.1 V at 973 K. To optimize the operating conditions, the effects of the steam vapor pressure and hydrogen partial pressure on the electrochemical performance of the hydrogen pump were investigated. The steam in the sweep side was consumed by the steam electrolysis due to the partial oxygen conductivity. Therefore, supplying insufficient steam to the cathode was found to cause a steep increase in the voltage at high currents owing to a decrease in the proton conductivity.

An electrolyte supported solid oxide cell of 45 cm2 area was operated in the steam-electrolysis mode during more than 23,000 h before scheduled shutdown, of which 20,000 h with a current density of j = −0.9 A cm−2. The cell consisted of a scandia/ceria doped zirconia electrolyte (6Sc1CeSZ), CGO diffusion-barrier/adhesion layers between electrolyte and electrodes, a lanthanum strontium cobaltite ferrite (LSCF) oxygen electrode, and a nickel/gadolinia-doped ceria (Ni/GDC) steam/hydrogen electrode. Voltage degradation in the operation period with j = −0.9 A cm−2 was 7.4 mV/1000 h (0.57%/1000 h) and the increase in the area specific resistance 8 mΩ cm2/1000 h. The final cell voltage was 1.33 V (at 851 °C cell temperature). After dismantling, the cell showed no mechanical damage at electrolyte and H2/H2O electrode; a small fraction of the oxygen electrode was delaminated. Impedance spectroscopy applied at the steady state DC current density confirmed a degradation dominated by an increasing ohmic term, mainly due to ionic conductivity decay in the electrolyte. In addition, a small non-ohmic and at least partly reversible O2 electrode contribution to degradation was identified, affected by a pollution from the (compressor) purge air.

N-doped mildly oxidized CNTs (moCNTs) catalysts for oxygen reduction reaction in proton exchange membrane fuel cells were prepared by a two-step method consisting of polymerization and pyrolyzation. The morphology of the electrocatalyst samples were characterized by scanning electron microscopy (SEM), high resolution transmission electron microscopy (TEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). It was discovered that the N-doped moCNTs catalyst showed a graphene-like nanosheets nanostructure; electrocatalytic properties of the catalysts were investigated by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). The experimental results exhibited remarkable catalytic activity in an acidic medium, with the onset potential, half-wave potential, and limiting current density reaching 0.87 V, 0.75 V (vs. reversible hydrogen electrode), and 3.5 mA/cm2, respectively. It can be concluded that the high catalytic performance is due to the high content of graphitic nitrogen and the graphene-like nanosheets structure.

Hydrogen storage/evolution behavior of nafion/NaCl/graphene quantum dot (GQD) mixed matrix as selective hydrogen capacitor (power source) was evaluated in detail through an electrochemical process at two independent potential ranges. For this purpose, a three-electrode system included Pt disk as counter electrode, Ag/AgCl as reference electrode and GQD-based mixed matrix-modified Pt disk as working electrode. For hydrogen storage, the deposition potential and time were evaluated to −1.0 V (vs. Ag/AgCl) and 120 s, respectively under high basic solution generated using NaOH (1.0 M) solution, followed by evolution of hydrogen at +0.8 V (vs. Ag/AgCl) during formation of hydrogen bubbles. The main advantage of this system was the occurrence of hydrogen storage and evolution at two independent potential windows. Both mass transfer and adsorption processes were estimated for the tensammetric peak during the evolution step. The mechanism of hydrogen storage and evolution was obeyed from diffusion and tensammetry, respectively. According to Randles–Sevcik equation using 1.0 mM Fe ( CN ) 6 3 − / 4 − , the active surface area of nafion/NaCl/GQD mixed matrix was ∼1906 m2g−1. Based on the CHN analyses, pressure-concentration temperature as well as hydrogen temperature-programmed desorption, the capacity of the synthesized GQDs for hydrogen storage and evolution was estimated to at least 10.1 and 8.6 wt%, respectively. The stability of the electrode was also estimated during 7000s by chronoamperometry during applying at least 40 cycles in the range from −1.0 to +1.3 V with reproducible tensammetric peak current (relative standard deviation: 2.54%).

The non-precious metal catalysts usually have low nitrogen content, resulting in poor oxygen reduction reaction (ORR) performance. Herein we demonstrated a strategy to synthesize the Fe/N/C carbon nanotubes (Fe–N–BCNTs) with high nitrogen content. The strategy included pyrolysis of ferric chloride and dicyandiamide, polymerization of pyrrole onto intermediate product's surface, and following by calcination in N 2 atmosphere. Electrochemical test results show that the catalyst exhibits highly efficient ORR activity with an onset potential of 0.995 V ( vs reversible hydrogen electrode) in 0.1 M KOH solution, 30 mV more positive than that of 20 wt. % Pt/C catalyst. The excellent ORR performances could be attributed to the more nitrogen functional groups in Fe–N–BCNTs-PPy-800 catalyst, which is revealed by Raman and XPS. Moreover, the prepared catalyst exhibits better methanol tolerance and higher stability in comparison to commercial Pt/C catalyst.

The research and developments of porous, highly active non-noble metal cathode materials are the current hot spots. In our work, ZIF-9 (Zeolitic imidazolate framework-9) as a cobalt source provide porous structure, we have sulfurized the ZIF-9 into CoS 2 by a simple hydrothermal method. Ultimately, the porous CoS 2 /RGO cathode material was obtained. Through a series of characterization analyses (powder X-ray diffraction, X-ray photoelectron spectroscopy), it is confirmed that the CoS 2 /RGO composite was successfully formed. Furthermore, electrochemical tests demonstrated that the pursued catalyst exhibited remarkable hydrogen evolution reaction (HER) activities with a favorable overpotential (only 180 mV for 10 mA cm −2 vs reversible hydrogen electrode), a low Tafel slopes (75 mV decade −1 ) and high stability in acidic condition (more than 18 h).

Reversible solid oxide cells (RSOCs) can work for power generation by converting fuel chemical energy to electric energy as solid oxide fuel cells (SOFCs) and for hydrogen production by converting excess electrical power to chemical energy as solid oxide electrolysis cells (SOECs). In this work, the possibility of using impregnated La0.8Sr0.2Co0.8Ni0.2O3−δ-Ce0.9Gd0.1O2−δ (LSCN-GDC) as oxygen electrode in RSOCs is investigated. The button cells with Ni-YSZ hydrogen electrode, YSZ electrolyte and impregnated LSCN-GDC oxygen electrode are fabricated. In the SOFC mode, cell with impregnated LSCN-GDC electrode shows an impressive power density of 1.336 W cm−2 at 800 °C and the polarization resistance is 0.100 Ω cm2 under open circuit condition, approximately the same as the value in the SOEC mode at applied current density of 0.2 A cm−2. In the SOEC mode, the variable operating parameters are optimized to obtain the maximum hydrogen production and minimum energy consumption. The remarkable current density reaches 2.34 A cm−2 at 1.6 V when measured at 800 °C with 90 vol% absolute humidity (AH). The polarization degradation behavior of LSCN-GDC oxygen electrode under electrolysis mode is analyzed in detail by estimating the three-phase boundary (TPB) change of the oxygen electrode.

The aim of the present work was to examine the processes of hydrogen sorption/desorption occurring in alkaline solution for electrodes made of EG/Ni/Pd (exfoliated graphite/nickel/palladium) composite. The electrochemical investigations were carried out using cyclic voltammetry technique accompanied by the potentiostatic polarization of electrode material at negative potential. To saturate the electrode with hydrogen, when an electrode reached the potential of −1.2 V, the potential was stopped for a chosen time. After that the potential scanning was continued. Anodic charge insignificantly increases with increasing the hydrogen sorption duration, whereas the changes in shape as well as in location of anodic peaks noted in response to the cathodic reactions of hydrogen sorption are much more pronounced. It indicates that mechanism and kinetics of the oxidation/desorption processes are altered due to increase in sorption time. The SEM (scanning electron microscopy) equipped with EDS (energy dispersive spectrometer) detector and XRD (X-ray diffraction) analysis were used to characterize the investigated composite material.

If a molten carbonate electrolysis cell (MCEC) is applied for fuel gas production it is important to know the polarization of the nickel electrode when operated at low concentration of hydrogen. Thus, the electrochemical performance of the Ni electrode was investigated under hydrogen-lean gases containing 1/24.5/24.5/50%, 1/49.5/24.5/25%, 1/24.5/49.5/25% and 1/49.5/49.5/0% H2/CO2/H2O/N2 in the temperature range of 600–650 °C and was then compared to the reference case with 25/25/25/25% H2/CO2/H2O/N2. The electrochemical measurements included polarization curve coupled with current interrupt, and electrochemical impedance spectroscopy. Polarization resistances of the Ni electrode obtained by the two different techniques agreed well. For the inlet gases containing low amounts of hydrogen the Ni electrode exhibited higher polarization losses than when using the reference case in the electrolysis cell. The electrochemical impedance measurements showed that both charge-transfer and mass-transfer polarizations were higher for hydrogen-lean gases at all measured temperatures. Except under the condition with 1/49.5/49.5% H2/CO2/H2O at 650 °C, the Ni electrode exhibited lower mass-transfer polarization when compared to the reference case. Furthermore, the mass-transfer polarization was strongly dependent on temperature under H2-lean gases, differing from the reference case when the temperature has almost no effect on mass-transfer polarization. The activation energy for hydrogen production was calculated to be in the range of 69–138 kJ·mol-1 under all measured gases, indicating that the Ni electrode is under kinetic and/or mixed control in the MCEC. QC 20160419

A novel photoelectrochemical (PEC) cell design is proposed and investigated for H-2 production with gaseous reactants. The core of the cell is a membrane electrode assembly (MEA) that consists of a TiO2 nanotube arrays photoanode, a Pt/C cathode, a Pt/C reference electrode and a proton conducting polymeric electrolyte membrane (PEM), which serves both as compact reactor for water splitting and as gas separator. The design is inspired by PEM electrolysis technology and modified appropriately to allow light irradiation and to host a third electrode compartment, which enables the use of a hydrogen reference electrode. The titanium dioxide nanotube arrays (TNTAs) photoanodes were synthetized, for the first time, on a Ti-web of microfiber substrates by electrochemical anodization. The performance of TNTAs/Ti-web photoanodes were evaluated in both gaseous (i.e. PEM-PEC cell) and liquid media (conventional PEC cell). Due to the presence of the PEM-PEC reference electrode comparison of the results was possible. Gas phase operation with either He or air as carrier exhibits very promising photoefficiency in comparison with conventional PEC cells. Additionally the performance of our PEM-PEC cell was also investigated for simultaneous anodic air treatment and cathodic hydrogen evolution. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

The corrosion stability of a series of carbon supports of various porous structure and morphology: commercial carbon blacks, carbon–carbon composite, and multiwall carbon nanotubes was studied using start-stop protocol cycling (1–1.5 V vs reversible hydrogen electrode (RHE) potential range with 0.5 V/s of scan rate) in an electrochemical cell at 25 °C using 0.1 M HClO 4 as electrolyte. Two stability regions were revealed for the first time depending on the cycle number. The first one is characterized by a constant value of quinone/hydroquinone (QH) transition potential. In the second part anode and cathode QH peaks gradually shift toward higher and lower potentials respectively, which is due most likely to a complete degradation of the supports. We proposed an effective resistance (R eff ) as the corrosion stability parameter that can be easily obtained from the cyclic voltammetry (CV) data. Based on these results, a model of corrosion of porous carbon materials supported on glassy carbon rod was proposed. It was shown that the decrease in the R eff of the samples in the initial stages of degradation is due to the increase in the number of QH groups on the surface, while a sharp increase in the R eff upon further cycling can be explained by a decrease in the number of contacts between the carbon grains.