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Electrochemical CO2 Reduction (CO2R) in acidic electrolytes has gained significant attention owing to higher carbon efficiency and stability than in alkaline counterparts. However, the proton source and the role of alkali cations for CO2R are still under debate. By using rotating ring disk electrode and surface‐enhanced infrared absorption spectroscopy, we find that a neutral/alkaline environment at the interface is necessary for CO2R even in acidic electrolytes. We also confirm that water molecules, rather than protons serve as the proton source for CO2R. Alkali cations in the outer Helmholtz plane activate H2O and promote the desorption of adsorbed carbon monoxide. Additionally, the solvated CO2, or CO2(aq), is the actual reactant for CO2R. This study provides a deeper understanding of the electrode/electrolyte interface during CO2R in acidic electrolytes and sheds light on further performance improvement of this system. [ABSTRACT FROM AUTHOR]

High‐performance bifunctional electrocatalysts for the oxygen reduction (ORR) and oxygen evolution reaction (OER) are essential components in energy conversion and storage technologies. Yet, their poor reversibility hinders their applicability. A highly active ORR/OER catalyst, consisting of multiwalled carbon nanotubes‐supported MnFeNiOx nanoparticles, was subjected to sequences of chronoamperometric steps alternating between the ORR, the OER and highly cathodic potentials (Ec). Rotating ring disk electrode methods revealed that applying Ec leads to a small increase in the current and peroxide species yield during the ORR while enhancing substantially the OER. X‐ray absorption spectroscopy showed irreversible changes in the chemical state of MnFeNiOx correlating with its catalytic properties. The complexity of changes that a composite catalyst may undergo under varying potentials, the importance of monitoring product formation, and the convenience of using dynamic electrochemical sequences for the assessment of catalyst reversibility, as well as for the activation and/or restoration of their catalytic properties, are highlighted. [ABSTRACT FROM AUTHOR]

The controlled growth of surface‐modifying polymer films by electrodeposition often fails because of the lack of redox activity of these compounds. Here, electroactive complexants help to electrodeposit non‐electroactive polymers. Hence, we investigate the counterion‐induced electrodeposition of polyelectrolytes: three quaternized poly(N,N‐dialkylaminoethyl methacrylate)s (qPDAAEMA), in particular their methyl, ethyl, and isopropyl derivatives (i. e. qPDMAEMA, qPDEAEMA, and qPDPAEMA), provide transparent solutions in the presence of hexacyanoferrate(II) (ferrocyanide) at specific concentration windows of the KCl supporting electrolyte. Below a certain KCl concentration, insolubility dominates irrespective of the hexacyanoferrate valency, whilst above an upper threshold, full solubility is observed. Between these limits, oxidation reversibly electrodeposits polymer/hexacyanoferrate(III) (ferricyanide) complexes. Hydrodynamic voltammetry (and data analysis using in‐house software) provides access to the deposition efficiency (DE). qPDEAEMA with ethyl substituents shows highest DEs; larger or smaller substituents fall short because of a balance between "hydrophobicity" and charge separation, shifting the window toward smaller salt concentrations with increasing alkyl size. We always observe a DE maximum close to the minimum salt concentration, whilst electrochemical quartz crystal microbalance (EQCM) measurements indicate a change in film water content close to the maximum. These effects, being also discussed in terms of polymer conformation, can direct the future engineering of electroassisted coatings. [ABSTRACT FROM AUTHOR]

Abstract The controlled growth of surface‐modifying polymer films by electrodeposition often fails because of the lack of redox activity of these compounds. Here, electroactive complexants help to electrodeposit non‐electroactive polymers. Hence, we investigate the counterion‐induced electrodeposition of polyelectrolytes: three quaternized poly(N,N‐dialkylaminoethyl methacrylate)s (qPDAAEMA), in particular their methyl, ethyl, and isopropyl derivatives (i. e. qPDMAEMA, qPDEAEMA, and qPDPAEMA), provide transparent solutions in the presence of hexacyanoferrate(II) (ferrocyanide) at specific concentration windows of the KCl supporting electrolyte. Below a certain KCl concentration, insolubility dominates irrespective of the hexacyanoferrate valency, whilst above an upper threshold, full solubility is observed. Between these limits, oxidation reversibly electrodeposits polymer/hexacyanoferrate(III) (ferricyanide) complexes. Hydrodynamic voltammetry (and data analysis using in‐house software) provides access to the deposition efficiency (DE). qPDEAEMA with ethyl substituents shows highest DEs; larger or smaller substituents fall short because of a balance between “hydrophobicity” and charge separation, shifting the window toward smaller salt concentrations with increasing alkyl size. We always observe a DE maximum close to the minimum salt concentration, whilst electrochemical quartz crystal microbalance (EQCM) measurements indicate a change in film water content close to the maximum. These effects, being also discussed in terms of polymer conformation, can direct the future engineering of electroassisted coatings.

Fuel cells and metal–air batteries hold significant promise to help decarbonize transportation and the electricity grid. To encourage widespread adoption of these technologies, improvements to their air-breathing cathodes are required, which address problems such as the high cost of platinum (Pt) catalysts used to boost the kinetics of the oxygen reduction reaction (ORR) as well as the stability of Pt/C interfaces over long-term cycling. In this paper, we demonstrate a facile approach to reduce Pt content to less than 2 wt % by interfacing Pt with CoOx as well-dispersed nanoparticles entrapped within a highly conductive laser-induced graphene (LIG) matrix. Laser-induced carbonization of polymerized furfural alcohol preloaded with Co and Pt precursors resulted in the formation of a mixture of spherical nanoalloys PtCoOx and core (CoOx)–shell (Pt) structures. This LIG-PtCoOx electrode exhibited a low onset and half-wave potential in alkaline media, which closely approached a benchmark Pt/C. The effectiveness of LIG-PtCoOx was demonstrated by its performance in rotating disk and rotating ring disk electrode studies versus commercial Pt/C with the same concentration of the catalyst, which resulted in 4-fold greater mass activity and more than 6-fold higher specific activity, which are reflected in a high turnover frequency (TOF). The resulting material was tested as an air–cathode for zinc (Zn)–air batteries leading to improved stability (118 h of operation) and rechargeability (0.75 V voltage gap), exhibiting a higher peak power density compared to batteries assembled with the commercial benchmark Pt/C cathodes with similar composition. [ABSTRACT FROM AUTHOR]

The reduction of selenate, SeO 4 2 − (a q) , in 0.1 M HClO 4 solutions, induced by underpotential deposition, UPD, of Cu on polycrystalline Au electrodes was investigated using the rotating ring-disk electrode, RRDE, technique. Design and implementation of electrode potential-rotation rate protocols made it possible to determine the rates of SeO 4 2 − (a q) reduction as a function of Cu coverage, θ Cu , as determined by the Bruckenstein method (Swathirajan et al. J. Phys. Chem. 1982, 86 , 2480–2485). In agreement with the results reported recently for Au(111) film electrodes (Strobl et al. Electrochimica Acta 2024, 493 , 144,298), the reaction was found to proceed only for θ Cu above a critical value, i.e. ca. 0.39, in this case, and the mechanism is consistent with an initial reversible formation of adsorbed Cu | SeO 4 2 − (a d s) , followed by its subsequent irreversible reduction, to yield a yet to be identified species denoted as Cu | Se (a d s) , as the rate determining step. Best fits of the kinetic model yielded values of the equilibrium constant for adduct formation, K, and first order rate constant for adduct reduction, k ET , in the range (2.4 – 45) × 106 cm3 mol−1 and (0.55 – 30) × 10−3 s−1, respectively, which are close to those found for Au(111). This unique electrocatalytic effect has been attributed to a shift in the potential of zero charge of the bare substrate toward more negative values, induced by the metal UPD, which promotes the adsorption of the oxyanion at potentials more negative than those found for the bare substrate, making it possible to access overpotentials large enough for its further reduction to ensue. [ABSTRACT FROM AUTHOR]

Platinum group metal-free (PGM-free) catalyst with different loadings was investigated in air breathing electrodes microbial fuel cells (MFCs). Firstly, the electrocatalytic activity towards oxygen reduction reaction (ORR) of the catalyst was investigated by rotating ring disk electrode (RRDE) setup with different catalyst loadings. The results showed that higher loading led to an increased in the half wave potential and the limiting current and to a further decrease in the peroxide production. The electrons transferred also slightly increased with the catalyst loading up to the value of ≈3.75. This variation probably indicates that the catalyst investigated follow a 2x2e- transfer mechanism. The catalyst was integrated within activated carbon pellet-like air-breathing cathode in eight different loadings varying between 0.1 mgcm-2 and 10 mgcm-2. Performance were enhanced gradually with the increase in catalyst content. Power densities varied between 90 ± 9 μWcm-2 and 262 ± 4 μWcm-2 with catalyst loading of 0.1 mgcm-2 and 10 mgcm-2 respectively. Cost assessments related to the catalyst performance are presented. An increase in catalyst utilization led to an increase in power generated with a substantial increase in the whole costs. Also a decrease in performance due to cathode/catalyst deterioration over time led to a further increase in the costs.

Oxide-derived zinc, an abundant and cost-effective electrode material alternative to gold and silver, has exhibited high activity for the electroreduction of CO 2 to CO (CO 2 RR). However, the impact of cations on the CO 2 RR activity remains unexplored. In this study, we investigated the effect of three alkali metal cations (Cs+, K+, and Li+) on the CO 2 RR over a ZnO nanorod electrode, using a rotating ring disk electrode (RRDE) technique. Cyclic voltammetry of the Pt ring in the RRDE tip reveals a consistent trend in the buffering capacity of these cations (Cs+ > K+ > Li+), as evidenced by the availability of OH⁻ ions for CO electrooxidation and hydrogen oxidation reactions (HOR). Cs+ showed a pronounced effect on the activity of the CO 2 RR to CO since it can regulate OH⁻ concentration and maintain the local pH. This study addresses the ongoing debate concerning the effects of cations; interfacial electric field and buffering capacity; and elucidates the relationship among electrolyte/cation, local pH dynamics, and the CO 2 RR activity towards CO over the active oxide-derived Zn electrodes, all derived from the fast and facile RRDE technique. [ABSTRACT FROM AUTHOR]

M1-M2-N-C bimetallic catalysts with M1 as Fe and Co and M2 as Fe, Co, Ni and Mn were synthesized and investigated as cathode catalysts for oxygen reduction reaction (ORR). The catalysts were prepared by Sacrificial Support Method in which silica was the template and aminoantipyrine (AAPyr) was the organic precursor. The electro-catalytic properties of these catalysts were investigated by using rotating ring disk (RRDE) electrode setup in neutral electrolyte. Fe-Mn-AAPyr outperformed Fe-AAPyr that showed higher performances compared to Fe-Co-AAPyr and Fe-Ni-AAPyr in terms of half-wave potential. In parallel, Fe-Co-AAPyr, Co-Mn-AAPyr and Co-Ni-AAPyr outperformed Co-AAPyr. The presence of Co within the catalyst contributed to high peroxide production not desired for efficient ORR. The catalytic capability of the catalysts integrated in air-breathing cathode was also verified. It was found that Co-based catalysts showed an improvement in performance by the addition of second metal compared to simple Co- AAPyr. Fe-based bimetallic materials didnt show improvement compared to Fe-AAPyr with the exception of Fe-Mn-AAPyr catalyst that had the highest performance recorded in this study with maximum power density of 221.8 ± 6.6 μWcm-2. Activated carbon (AC) was used as control and had the lowest performances in RRDE and achieved only 95.6 ± 5.8 μWcm-2 when tested in MFC.

The rotating ring disk electrode (RRDE) with a Pt ring is widely applied for oxygen reduction reaction (ORR) studies, and it is generally believed that oxidation of H2O2 at the Pt ring is controlled by diffusion. Indeed, H2O2 oxidation at bare platinum is a diffusion‐controlled reaction. However, when Pt ring is held at 1.2 VRHE, it is being covered with surface oxide, and H2O2 oxidation turns into a reaction under mixed diffusion‐kinetic control. We show that, for H2O2 oxidation at an oxide‐covered Pt ring in 0.1 M KOH, the ratio of the empirical ring current to corresponding ring current under pure diffusion control varies monotonically with rotation rate. At 1.2 VRHE, the ratio is equal to 79.9 % and 61.4 % at 400 rpm and 2500 rpm, respectively. We demonstrate that this deviation prevents the correct diagnosis of ORR mechanism and leads to overestimated electron transfer number values. To eliminate the error in RRDE measurements, we employed a procedure based on the Koutecký‐Levich method, which, to our best knowledge, has not been reported yet. [ABSTRACT FROM AUTHOR]

The effect of H 2 S contamination on platinum catalyst has been investigated in terms of rotating ring disk electrode measurements (RRDE) in 0.1 M HClO 4. The electrochemical surface area (ECSA) was determined by hydrogen underpotential deposition (HUPD) and CO stripping methods before and after accelerated stress tests (AST). The observed reduced losses of ECSA of the catalyst in the presence of H 2 S were associated to adsorbed sulphuric compounds on the catalyst surface which changed electrochemical characteristics of the materials surface. The RRDE experiments revealed that for oxygen reduction reaction (ORR) mass and specific activities were essentially decreased after AST with H 2 S contamination which was attributed to the interstitial defect on platinum atom sites due to adsorbed sulphuric compounds. Identical location and high resolution transmission electron microscopy (TEM) analysis have revealed only slightly different catalyst surface morphology and particle sizes before and after the AST indicating rather atomic scale deterioration of the platinum catalyst surface due to the adsorbed sulphur species. • H 2 S leads to a lowered ECSA by blocking of electrochemical active catalyst sites. • Sulphuric species influence towards stronger H 2 O 2 formation. • H 2 S impacts on the ORR mechanism towards the unfavourable 2-electron-pathway. • Negligible impact of H 2 S on Pt particle disappearance and agglomeration is evidenced. [ABSTRACT FROM AUTHOR]

Electrocatalytic active species like transition metal oxides have been widely combined with carbon-based nanomaterials for enhanced Oxygen Reduction Reaction (ORR) studies because of the synergistic effect arising between different components. The aim of the present study is to synthesize CeO2/g-C3N4 system and compare the ORR activity with bare CeO2. Ceria (CeO2) embedded on g-C3N4 nanocomposite was synthesized by a single-step microwave-mediated solvothermal method. This cerium oxide-based nanocomposite displays enhanced ORR activity and electrochemical stability as compared to bare ceria.

Oxygen reduction reaction (ORR) in Proton Exchange Membrane Fuel Cell (PEMFC) is the most sluggish reaction, which impedes the performance and commercialization of PEMFC. Platinum-based alloys show higher ORR activity than Pt and it is suggested by density functional theory calculations that Pt 3 Sc alloy has high stability and higher ORR activity due to filling the metal d-bands and lowers binding energy of the oxygen species respectively. Herein, we report Pt 3 Sc alloy nanoparticles (NPs) dispersed over partially exfoliated carbon nanotubes (PECNTs) as a cathode catalyst for single-cell measurements of PEMFC where Pt 3 Sc alloy shows a lower binding energy towards oxygen and facilitates ORR with much faster kinetics. The ORR activity of Pt 3 Sc/PECNTs electrocatalyst, investigated by cyclic voltammetry, Rotating Disk electrode (RDE) and Rotating Ring Disk electrode (RRDE), shows the higher mass activity and lower H 2 O 2 formation than the commercial catalyst Pt/C-TKK. Accelerated Durability Tests (ADT) was performed to evaluate the stability of catalysts in acidic medium. In single-cell measurements, Pt 3 Sc/PECNTs cathode catalyst exhibits a power density of 760 mW cm−2 at 60 °C. Our study gives an important insight into the design of a novel ORR electrocatalyst with an excellent stability and high power density of PEMFC. Pt 3 Sc supported by partially exfoliated carbon nanotubes shows the higher mass activity and stability as an oxygen reduction reaction catalyst. Image 1 • Pt 3 Sc alloy nanoparticles supported PECNTs electrocatalyst has been synthesized. • Pt 3 Sc/PECNTs as an ORR electrocatalyst shows good catalytic activity and durability. • Synergy between 1D and 2D morphology of PECNTs helps in improving the durability of the catalyst. • The maximum power density obtained for Pt 3 Sc/PECNTs cathode electrocatalyst is 760 mW cm−2 at 60 °C without back pressure. [ABSTRACT FROM AUTHOR]

Abstract A simple method to prepare a dendritic Pt-shell coating on concave Pd nanoparticles (NPs) was successfully developed. In this study, tuning the Pt precursor concentration in the reaction mixture allowed control over the length of the outer Pt dendrites, enclosed by (211) high-index facets or (110) facets were performed. The concave Pd NPs covered by short Pt dendrites (Pd/S-Pt) and long Pt dendrites (Pd/L-Pt) were applied as catalysts for the oxygen reduction reaction (ORR) in 0.1 M HClO 4 electrolyte solution. Pd/S-Pt with (211) facets had higher specific activity (0.106 mA cm−2) than that of Pd/L-Pt with (110) facets (0.066 mA cm−2) or commercial Pt/C (0.076 mA cm−2). Additionally, the accelerated durability test (ADT) results revealed that the decay for the ORR kinetic current catalysed by Pd/S-Pt was 28.21%, which was smaller than that of Pt/C (58.15%). Thus, Pd/S-Pt was effective for catalysis of the ORR. Graphical abstract Image 1 Highlights • Dendritic Pt-shells coating on concave Pd NPs are successfully prepared. • Pt dendrites with short (Pd/S-Pt) or long chain length (Pd/L-Pt) are prepared. • Pd/S-Pt shows high ORR current in a mixed control of activation-diffusion period. • The specific activity of Pd/S-Pt is 1.39 times greater than that for Pt/C. • ADT results show that the stability of Pd/S-Pt is superior to Pt/C. [ABSTRACT FROM AUTHOR]

l -Cysteine ( l -Cys) is an amino acid of high interest in the electrochemical field since it is one of the five electrochemically active amino acids. Due to the S atom on its side chain, this molecule presents the highest amount of possible oxidation states. The rotating ring disk electrode (RRDE) technique is a very useful method for the investigation of complex mechanisms, such as l -Cys oxidation, as it allows the identification of some intermediates. By rotating disk electrode (RDE), it was possible to observe that the adsorption of l -Cys onto Pt electrodes is influenced by mass transport. The chemical reaction was found to be reversible, while the charge transfer irreversible. The RRDE study facilitated the proposal of an electrochemical-chemical-electrochemical mechanism. The ring current was observed to be dependent on the quadratic of the potential applied to the disk electrode combined with the value of the rotation rate in a soft-model algorithm. The product of this chemical step was oxidized in two steps on the ring, with the first one including the generation of an adsorbed intermediate as the rate-limiting step. [ABSTRACT FROM AUTHOR]

Five different bimetallic non-precius metal catalysts for oxygen reduction reaction (ORR) are synthesized by different combinations of two transition metal (Fe, Co, Cu, Zn) phthalocyanine precusrsors. The aim of this study is to investigate the effects of the different combinations of two transition metals on the physico-chemical and ORR electrocatalytic activity of the catalysts. The precursors were mixed, impregnated on a mesoporous silica used as a hard template, and pyrolyzed under inert atmosphere at 800 °C. After the template removal, the catalysts were characterized via BET, FESEM, and XPS. TGA-MS analysis was also performed on the catalysts precursors to simulate their behaviour during the pyrolysis, detecting the evolved gases. The results show that both the physico-chemical features and the ORR activity and selectivity in acidic medium (measured by RDE-RRDE technique) are strongly influenced by the transition metals pair used. In particular, the most effective transition metals pair to get a more performing ORR catalyst is Co-Zn. The catalysts are also tested in direct methanol fuel cell, including a short-term durability test. The durability of the best perfroming Co-Zn catalyst is improved compared to a similar catalyst synthesized using Fe. The possibility of tuning the catalysts features by combining different transition metals enables to increase the catalyst durability, the production yield during the synthesis (enabling to recover more material after the pyrolysis), and the surface N fixation. [ABSTRACT FROM AUTHOR]

An ex-situ evaluation of the effects of Ca 2+ on the cathode of proton exchange membrane fuel cells was completed. A Ca 2+ concentration of 0.9 mM in the HClO 4 solution had no effect on the oxygen reduction reaction activity of a Pt/C catalyst. Upon increasing the Ca 2+ concentration to 9 and 90 mM, the availability of Pt active sites slightly decreased in the presence of Ca 2+ , and other observed effects included (i) a decrease in the kinetic and diffusion-limited currents; (ii) a decrease in the electron transfer number, and accordingly, an increase in H 2 O 2 formation; and (iii) an increase in the acid site occupation and a decrease in the O 2 permeability in the ionomer. The Ca 2+ cations that were absorbed in the ionomer reduced the mass-transport kinetics of O 2 and blocked the adsorption of O 2 on the Pt particles. [ABSTRACT FROM AUTHOR]

[Display omitted] • Rare earth SmMnO 3 perovskite was prepared by hydrothermal synthesis methods at 200 °C. • The catalytic activity of SmMnO 3 towards oxygen reduction reaction in an alkaline medium was studied. • The onset potential and current calculated for the prepared catalyst is close to the commercial Pt/C. • This work provides a useful exploration for the development of a stable, efficient catalyst that has the potential to replace commercial Pt/C. The present study elucidates the catalytic activity of SmMnO 3 towards oxygen reduction reaction in an alkaline medium. Rare earth SmMnO 3 perovskite was prepared by hydrothermal synthesis method. The structure, morphology, composition and particle size of the synthesized material were determined by different analytical tools such as XRD, FTIR, SEM, TEM and XPS. To improve the electrical conductivity of the prepared catalyst, vulcan carbon (VC) was added during the ink preparation. Oxygen reduction reaction (ORR) activities of the prepared catalyst were studied in alkaline medium. The catalytic performances were studied with a rotating ring disc electrode (RRDE). A linear sweep voltammetric graph was plotted and compared with commercial Pt/C. The onset potential and current density calculated for the prepared catalyst is close to the commercial Pt/C. The stability and methanol tolerance showed better activity of the prepared catalyst as compared to commercial Pt/C. This work provides a useful exploration for the development of a stable, efficient catalyst that has the potential to replace commercial Pt/C. [ABSTRACT FROM AUTHOR]

In this work, we study the mechanism and kinetics of the oxygen reduction reaction (ORR) over Pd/C, Pd 2 Co/C and PdCo 2 /C electrocatalysts synthesized by thermal reduction of organometallic precursors, such as [Pd 3 (μ-3-Ph-pz) 6 ], [Et 4 N] 2 [Pd 2 Co(μ-4-I-3,5-Me 2 -pz) 4 Cl 4 ], and [Et 4 N] 2 [PdCo 2 (μ-4-I-3,5-Me 2 -pz) 4 Cl 4 ]. The methanol tolerance and formation of peroxide under oxygen reduction reaction conditions were determined using a rotating disk electrode (RDE) and a rotating ring disk electrode (RRDE). The Pd 2 Co/C catalysts prepared from [Et 4 N] 2 [PdCo 2 (4-I-3,5-Me 2 -pz) 4 Cl 4 ] showed the best ORR activity and higher methanol tolerance, compared with commercial platinum catalysts. The ORR electron transfer number for Pd 2 Co/C was 3.7, similar to the Pd/C commercial catalysts. Compared to the commercial catalysts, Pd 2 Co/C and PdCo 2 /C showed the highest hydrogen peroxide formation (%H 2 O 2 ), 16 and 24%, respectively. Electrogeneration of hydrogen peroxide has potential application in advanced oxidation processes. [ABSTRACT FROM AUTHOR]

Abstract: Herein, we report a simple and elegant aqueous synthesis of Pd100‐xPtx (x=5, 10, 15 and 20) nano‐porous structures (NPoS) derived from Pd100‐xMn2x (x=5, 10, 15 and 20) nano‐alloys. Pd100‐xPtx/C NPoS exhibit enhanced oxygen reduction reaction (ORR) activity along with higher retention of figure of merit in the presence of methanol compared to HiSPEC Pt/C catalyst. The ORR mass and specific activity values of Pd100‐xPtx/C NPoS are high and exceed the U.S. department of energy (DOE) 2017–2020 targets. The enhanced methanol tolerance and ORR activity of Pd100‐xPtx/C NPoS is attributed to their unique surface active Pd−Pt islands on nano‐porous Pd. Direct methanol fuel cell performance studies employed using Pd85Pt15/C NPoS as cathode material (0.4 mgPt/cm2) and HiSPEC PtRu/C NPs as anode material (0.2 mgPt/cm2) shows improved direct methanol fuel cell (DMFC) single cell activity at low Pt loading and the results are presented. [ABSTRACT FROM AUTHOR]

Defective Pd@Pd-Pt nanocubes (NCs) were successfully synthesized by a displacement deposition method. In this study, a Pt layer was predominantly deposited at the corners and edges of Pd NCs to form concave NC surfaces and a Pd-Pt shell with a Pd-only core. Additionally, rotating ring-disk electrode experiments were performed to determine the mass activities of these Pd@Pd-Pt NCs, which acted as oxygen reduction catalysts in a KOH solution. The concave Pd@Pd-Pt NCs (28.2 nm) exhibited a 1.7-fold higher activity than that of 7 nm Pt nanoparticles. After accelerated durability tests, the data indicated the prepared NCs retained nearly 80% of the initial activity for the oxygen reduction reaction. [ABSTRACT FROM AUTHOR]

Different Me–N–C catalysts for oxygen reduction reaction (ORR) are synthesized using Me(II)-phthalocyanines (Me = Fe, Co, Cu, Zn) as a unique precursor molecule, and SBA-15 silica as a sacrificial template. The influence of different transition metals on the pyrolysis process and the consequent physical–chemical properties of the final catalysts were investigated using different characterization techniques such as N 2 physisorption, FESEM, EDX, XPS, XRD, and thermogravimetric analysis coupled with mass spectrometry (TGA-MS). The ORR activity and selectivity toward a complete 4-electrons reaction were assessed by RDE analysis in alkaline conditions. The ORR activity of the different Me–N–C catalysts decreases in the order Fe > Co > Cu > Zn ≈ H. Microporosity, pyridinic nitrogen content and temperature at which H 2 starts to be detected during the pyrolysis are directly related to the ORR activity of the different catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • RRDE was established as an online method to evaluate electrocatalyst performance. • Electrocatalysts active H 2 O 2 to produce •OH and subsequently generate O 2 •−. • Anodic currents on ring electrode due to O 2 •− oxidation were measured. • The RRDE method is verified by terephthalic acid fluorescence detection. One-electron electrochemical reduction of hydrogen peroxide (H 2 O 2) is an effective way to produce hydroxyl radical (•OH), whose yield is greatly dependent on the performance (activity and selectivity) of electrocatalysts. However, the current method to evaluate the performance of electrocatalysts is limited by time-consuming and less sensitive method of •OH detection. Herein, we propose an online rotating ring disk electrode (RRDE) method to evaluate the performance of electrocatalysts in H 2 O 2 activation by rapidly detecting •OH. This method is implemented by determining the current signals on the disk and ring electrodes: the generated •OH from H 2 O 2 reduction on the disk electrode (induce negative disk currents) reacts with H 2 O 2 to produce superoxide radical (O 2 •−), which migrates to and is oxidized on the ring electrode and generates positive ring currents. The relevance of the ring currents to O 2 •− and •OH is proved by radical quenching tests and kinetic analysis. The performance of five electrocatalysts were evaluated by both the RRDE method and the terephthalic acid (TPA) fluorescence method, and the consistent results verify the applicability of the RRDE method. Hence, this work facilitates the development of high-performance electrocatalysts for H 2 O 2 activation and bring insights for RRDE-based electroanalytic chemistry. [ABSTRACT FROM AUTHOR]

• The morphologies of catalyst films with different catalyst loadings were studied. • A low catalyst loading induced the coffee ring effect. • The coffee ring effect resulted in an underestimation of the performance parameters. • Catalyst overloading caused a higher oxygen transfer resistance and a lower ORR performance. • An optimal catalyst loading for commercial Pt/C was recommended. During the performance evaluation of electrocatalysts for the oxygen reduction reaction (ORR), the electrocatalysts are usually loaded on a rotation ring disk electrode (RRDE) to form a catalyst film (CF). To ensure accurate results, the CF must be as thin and even as possible to minimize the oxygen transport resistance within it. However, the catalyst loading used by recent publications varied significantly, preventing a direct comparison of the catalyst ORR performance between studies. In this study, a complementary metal-oxide-semiconductor (CMOS) camera and a Dektak XT profile meter are used to investigate the effect of Pt/C loading on the surface morphology, electrode coverage and average thickness, and thus the ORR performance of the CF. The results illustrate that the CF failed to completely cover the electrode surface at low catalyst loadings, which caused an underestimation of the limiting current density (J L), onset potential (E o n) and half-wave potential (E 1 / 2) of the catalyst. It is also determined that the deeper the Pt nanoparticles are located in the CF, the more likely the ORR performance of CFs is to be underestimated due to the increased oxygen transfer resistance. As a result, as the catalyst loading increased, the high viscosity of the catalyst ink led to particle agglomeration and an over-thickness at the center of the CF, which increased the inner oxygen transport resistance of the CF. This may not only slow the ORR kinetics of the catalyst, but also cause the ORR performance of the catalyst to be underestimated. Based on these findings, this study revealed the optimal catalyst loading (16.2–24.2 μg Pt cm−2) and a guided accurate measurement of the ORR catalyst. [ABSTRACT FROM AUTHOR]

The kinetics of oxygen reduction reaction (ORR) on carbon supported Pt, Pt-Sn, Pt-Ni, and Pt-Sn-Ni catalysts, prepared by Bönnemann method, is investigated by using rotating ring disk electrode (RRDE) measurements in 0.1 M HClO 4 solution. Physical characterization of the catalysts is performed by X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray (EDX) analysis and X-ray photoelectron spectroscopy (XPS) techniques. The cyclic voltammetry (CV) measurement has been used to estimate the electrochemical active surface (EAS) area of the catalyst. The enhancement in the ORR activity of the Pt/C observed in the presence of either Sn or Ni, leading to more than 99% of water formation. However, Pt-Sn/C catalyst shows a higher ORR performance as compared to the Pt-Ni/C and Pt-Sn-Ni/C catalysts. This can be explained by the presence of optimal amount of Sn oxides as an unalloyed state in Pt-Sn/C, which plays a beneficial role for both adsorption oxygen and water. On the other hand, it is found that the alloying Pt with Ni seems to be less favourable for the ORR performance. [ABSTRACT FROM AUTHOR]

• Catalysts based on nitrogen- and iron-doped carbon support (Fe-N-C). • High oxygen reduction activity in neutral pH. • Development of Fe-N-C air-breathing gas-diffusion electrodes. • Fe-N-C cathodes assembled in a single chamber microbial fuel cell. • High electrical power and voltage generation over time. This work reports the development of an iron-nitrogen-carbon electrocatalyst (Fe-N-C) synthesized by functionalization of carbon support using low-cost Fe- and N-based precursors in a wet impregnation procedure followed by a pyrolysis treatment under an inert atmosphere. Structure and surface chemistry were investigated by Raman and X-ray photoelectron spectroscopy (XPS), which indicated an efficient interaction of precursors with the carbon support during the wet-impregnations step, which allows obtaining a carbonized material with a high content of active sites based on Fe-N x moieties. This led to Fe-N-C materials with high catalytic activity towards oxygen reduction at neutral pH, as demonstrated by cyclic voltammetry (CV) and hydrodynamic linear sweep voltammetry with rotating ring disk electrode (LSV-RRDE). The Fe-N-C electrocatalyst was incorporated in air-breathing cathodes and performance was optimized in terms of oxygen reduction activity and stability. Such cathodes were assembled in single-chamber microbial fuel cell prototypes, and electrical power and voltage generation were evaluated over time. [ABSTRACT FROM AUTHOR]

Most of the past theoretical works with the rotating ring disk electrode (RRDE) system have been restricted to situations where supporting electrolyte concentration is large enough so that the effects of migration of ionic species in the solution becomes negligible. In this work, effects of ionic migration have been investigated for a RRDE system by solving the differential equations describing mass transfer in presence of ionic migration using numerical technique. Two cases were considered for simulation, presence and absence of migration of ionic species. Results indicate that in presence of migration, collection efficiency of a RRDE system increases for all electrode geometries and concentration boundary layer thickness reduces. Results also indicate that collection efficiency is dependent on electrode geometries. The system chosen for simulation is copper sulfate solution of 0.1 (M) concentration with little supporting electrolyte. It is also noticed that migration effect remains important for supporting electrolyte concentration as high as 0.1 (M). Limiting current condition was assumed. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1390-1399, 2013 [ABSTRACT FROM AUTHOR]

Abstract: The electroreduction of the pertechnetate ions has been examined in a wide range of sulfuric acid concentrations (0.5–4M) using electrochemical (CV, RRDE) and spectroelectrochemical UV–vis (Au-OTE) techniques. Soluble Tc(IV) and probably Tc(III,IV) species with absorption bands at 502nm and 670nm, respectively, were found to be formed during the reduction in 4M H2SO4. The strongly acidic medium was found to stabilize technetium forms with lower oxidation states. Spectroelectrochemical measurements performed in 4M H2SO4 show formation of [Tc(μ-O)2Tc]3+/4+. The results indicate existence of mixed chemical and electrochemical pathways of generation of Tc(IV) species, which can be later reduced to Tc(III,IV). Rotating ring disk electrode studies confirm generation of Tc-soluble species with lower oxidation states during pertechnetates reduction. The activation energy calculated for limiting current connected probably with generation of the dimeric structure of Tc in 4M H2SO4 is equal to 12.56±1.14kJmol−1 which can indicate a diffusion controlled process. [Copyright &y& Elsevier]

Abstract: The C-containing iron nitride electrocatalyst is fabricated by chelating N-containing species and Fe2+ with a carbon support under heat treatment in an NH3 atmosphere, which induces the oxygen reduction reaction activity. This is the first demonstration of forming Fe x C species on iron nitride materials. The correlation between the electrochemical properties and structures are aided to elucidate their features under investigation by using X-ray absorption spectroscopy. A rotating ring disk electrode test is conducted in sulfuric acid solution and the results reveal the low H2O2 yield and approximately 4e− transfer process of the carbon-containing FeN/C electrocatalyst. [Copyright &y& Elsevier]

Abstract: Nitrogen-doped carbon nanotubes (CN x ) were prepared via a floating catalyst chemical vapor deposition method using precursors consisting of ferrocene and melamine to control the nitrogen content. Structure, morphology and composition of all CN x catalysts were characterized by SEM, TEM, and XPS. These results indicated that the surface nitrogen content (up to 7.7at.%) increases with the increase of melamine used. Electrochemical methods were used to study the correlation between surface structure and the activity of oxygen reduction reaction (ORR) in acid and alkaline solutions. Electrochemical data indicated that the higher the nitrogen content is, the higher the oxygen reduction activity. Especially, the results from the rotating ring disk electrode technique demonstrated that CN x (7.7%) has similar ORR activity and selectivity with commercial Pt/C in alkaline solution. [ABSTRACT FROM AUTHOR]

In the manufacture of metal interconnects for semiconductor devices, trenches and vias in dielectric layers on the Si wafer are filled by copper electrodeposition. The acceleration of deposition at the bottom of trenches and vias is a key to the bottom-up filling of these high aspect ratio cavities. We report the detection of this acceleration effect by rotating ring disk electrode experiments. The Cu (I)-complex, which forms on the disk electrode, was captured as a current (Iring) on the ring electrode. Iring increased in periodic reverse pulse current mode, as compared to direct or pulse current. The periodic reverse pulse current produced the most bottom-up filling based on microscopic observations of via cross sections. Iring increased with the additions of Cl−, which also produced greater bottom-up filling. Iring increased with additions of SPS, which were also found to improve bottom-up filling. [ABSTRACT FROM AUTHOR]

In this work, various amine groups (ethylenediamine; EDA, tetraethylenepentamine; TEPA and polyethylenimine; PEI) functionalized 3D body-centered cubic mesoporous carbon materials (FDU16) were prepared to host sulfur to form FDU16-EDA/S, FDU16-TEPA/S and FDU16-PEI/S cathode materials for high performance Li S batteries. The materials were characterized by XRD, SAXS, SEM, TEM, Raman, EA, BET, CV and RRDE. The results showed that FDU16-PEI/S exhibited the largest initial discharge capacity of 1266 mAg g−1 at 0.1C and presented a lower capacity fading rate of 0.26% per cycle for the 100 cycles in comparison with the capacity fading rate of FDU16/S (0.41%), FDU16-EDA/S (0.31%) and FDU16-TEPA/S (0.29%). During the RRDE experiments, all samples revealed similar RRDE profiles in all disk voltage (DV) regions, suggesting they resemble the dissolution behavior of the LiPS intermediates during the cycling process. The FDU16-PEI/S owned a smaller slope value of ring current change in the DV II region, indicating a lower dissolution of LiPS intermediates from the sulfur electrode. The order of LiPS adsorption efficiency was shown to be PEI > TEPA > EDA. This study demonstrated carbon materials functionalized with large amine groups provide strong affinities with LiPS intermediates, resulting in notably improving cycle performance in Li S batteries. [Display omitted] • FDU16 with various amine-containing functionalities as sulfur host materials were fabricated. • An in situ RRDE is designed to study polysulfide dissolution behavior in Li S batteries. • LiPS trapping capability increased with the number of amine groups (EDA < TEPA < PEI). • Functionalization of PEI with FDU16 displays the best cycling performance. [ABSTRACT FROM AUTHOR]

Abstract: The kinetics of the oxygen reduction reaction (orr) on Cu(h k l) surfaces are investigated in perchloric acid and sulfuric acid solutions using rotating ring disk electrode (RRDCu(h k l)E). Parameters, such as reaction order, kinetic current, rate constant, Tafel slopes as well as the number of electrons transferred are determined. The variation in the activity and reaction pathway with the crystal faces in different electrolytes is related to the surface characteristics of Cu(h k l) and the structure-sensitive inhibiting effect of the adsorbed anions on their surfaces. In 0.1M HClO4, the difference in activity is clearly observed on Cu(h k l) surfaces (Cu(100)>Cu(111) although it is relatively small). The higher activity of Cu(100) arises from its more open characteristics which may facilitate the co-adsorption of O2. On the other hand, the adsorption of oxygenated species on Cu(111) at E >−0.35V induces a 2 e− pathway; while a 4 e− reduction is observed on Cu(100) in the entire potential region (−0.70V< E <−0.10V). In 0.5M H2SO4, the sequence in activity between Cu(111) and Cu(100) varies with the potentials, i.e., Cu(100) is initially more active than Cu(111) at −0.35V< E <−0.15V, however, the reversal in the activity between Cu(111) and Cu(100) is observed at more negative potentials (−0.45V< E <−0.35V). The desorption of strongly adsorbed (bi)sulfate anions on Cu(111) induces the 2 e− reduction via peroxide formation, however, a 4 e− reduction is dominant on the Cu(100) surfaces. The major effect of (bi)sulfate anions and oxygenated species on the orr kinetics and reaction pathway on Cu(h k l) surfaces is the blocking of active copper sites for the adsorption of O2 molecules. [Copyright &y& Elsevier]

O2 reduction has been performed at Au nanoparticle-electrodeposited Pt electrodes (Au/Pt electrodes) in O2–saturated 0.1 M KOH solution. Cyclic voltammetry (CV) and rotating ring-disk electrode (RRDE) techniques have been used in this investigation. Two reduction peaks were observed on the CV for the O2 reduction at the Au/Pt electrodes. The reduction pathway of O2 to either HO2− or OH− is highly dependent on the electrode potential and the Au surface coverage of the Pt electrode as well. The Au/Pt electrodes exhibit different electrocatalytic behaviour in three potential regions: At E>−300 mV, the 2-electron reduction of O2 to HO2− predominates, at −300>E>−500 mV, the 4-electron reduction predominates, and at E<−500 mV, the 2-electron and 4-electron reduction pathways proceed concurrently. The maximum production of HO2− (as a major reduction product) was obtained at a potential of ca. −240 mV versus Ag ∣ AgC ∣ KCl(sat), which is more positive by ca. 250 mV than the corresponding value at the bulk Au electrode (i.e. −500 mV vs. Ag ∣ AgCl ∣ KCl(sat)). The increase of the surface coverage of Au (i.e. increase of deposition time) on the Pt electrodes leads to a loss of this activity towards the O2 reduction to HO2−. At a relatively higher negative potential, i.e. at −400 mV, the 4-electron reduction of O2 to OH− occurs predominantly at all the examined Au/Pt electrodes with different Au loadings. Further negative increase of the potential (more negative than −400 mV) results in a partial contribution of the 2-electron reduction of O2 with the 4-electron reduction. This behaviour could be understood in view of the potential dependence of the amount and the nature of the adsorbed species on the Au/Pt disk electrode surface. [Copyright &y& Elsevier]

• Catalysts based on nitrogen- and iron-doped high surface area carbon support. • Effect of N-source and pyrolysis atmosphere on oxygen reduction rection (ORR). • Tailoring surface chemistry of active sites to enhance ORR in alkaline environment. • High durability over start-stop cycling tests. Fe-N-C catalysts were synthesized from a nitrogen and iron wet impregnation of carbon black pearls followed by pyrolysis steps. Three different nitrogen sources (dopamine, imidazole and benzimidazole), and two different pyrolysis atmospheres (Ar and NH 3) were used. The obtained materials were characterized in terms of structure, morphology, surface chemistry, and electrochemical properties. Electrodes with a high porosity and accessible active sites were obtained tailoring the synthesis parameters, as indicated by Raman and X-ray photoelectron spectroscopies, and cyclic voltammetry with rotating ring disk electrode. Pyrolysis under ammonia atmosphere led to high electrochemical active surface area (ECSA) and the use of imidazole as nitrogen-rich organic precursor improved oxygen reduction reaction (ORR) activity in alkaline pH. This can be ascribed to the modification of surface chemistry of the electrocatalysts triggered by the N-rich organic precursor and pyrolysis atmosphere. The catalyst obtained by using imidazole and pyrolyzed in NH 3 had a variety of iron-, oxygen- and nitrogen-functional groups, nitrogen being mainly distributed in imine-, pyridinic- and pyrrolic-N. In addition, durability tests showed a stable ECSA and ORR activity after cycling of the prepared electrocatalysts outperforming durability of Pt-based materials in alkaline environment and indicating applicability in anion exchange membrane fuel cells. [Display omitted] [ABSTRACT FROM AUTHOR]

Zn-polyiodide redox flow batteries (RFBs) are a promising grid-scale electrical energy storage (EES) option because of their significant energy density, which is due to the high solubility of ZnI 2 in water. In spite of the importance of the RFBs, a mechanistic understanding of both Zn2+/Zn and I 3 −/I− half redox reactions have not been fully achieved yet. The I 3 −/I− half redox reaction occurring on a cathode in this RFB is particularly complicated due to metastable iodine films, which only form on an electrode when an electrochemical potential is biased enough to drive the electro-oxidation of I−. Due to the thermodynamically unstable nature of iodine films in I−-rich aqueous solutions, the film is also difficult to characterize by ex-situ analyses, and its physicochemical properties are largely unknown. In this article, we report electrochemical in situ monitoring of the formation and dissolution of a metastable iodine film as an intermediate during I 3 −/I− redox reactions in an aqueous solution using a rotating ring disk electrode (RRDE). We suggested a reaction model for electro-oxidation of I− to I 3 − via iodine films and its electro-reduction to I− based on the mechanism proposed by Gileadi et al. Chronoamperograms (CAs) and cyclic voltammograms (CVs) associated with the I 2 /I− redox reaction involving only formation and dissolution of iodine films on a disk electrode were obtained using an RRDE. From the CAs and CVs, we successfully obtained trajectory information on the formation and dissolution of an iodine film during the I 3 −/I− redox reaction on a disk electrode under transient and potential-time variation conditions. In addition, we found evidence of a possible transition in the iodine film from an I−-conductor to an I−-semiconductor during formation based on the quantitatively monitored iodine formation curve as a function of time during electro-oxidation of I−. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• Cobalt–carbon core shells were established to be highly selective for 2 e− ORR pathway. • Co encapsulated N-carbon was used as electrocatalyst for the selective H 2 O 2 formation. • Rotating Ring Disk Electrode was used to rationalize structure/activity relationship. • The electrode implementation in a PEM static flow electrolyzer setup was investigated. The Oxygen Reduction Reaction (ORR) catalyzed by N-carbon electrocatalyst was investigated, focusing on the fundamental features for the selective H 2 O 2 formation. The electrochemical characterization was primarily performed by the use of the Rotating Ring Disk Electrode (RRDE) tool in both hydrodynamic Linear Sweep Voltammetry (LSV) mode and by Chronoamperometry (CA) measurement. We rationalized the structure/activity relationship, reaching a new state-of-the-art in terms of current density for the H 2 O 2 generation. The study also explored the performance in relation with the electrode deposit procedure that is of fundamental importance to achieve a suitable macroscopic electrode preparation. Furthermore, the electrode implementation in a polymer membrane static flow electrolyzer setup, was evaluated to understand how the material catalytic features such as current ranges and selectivity scale up from a classical three electrode system to a more realistic application-focused environment. [ABSTRACT FROM AUTHOR]