Step Of Hydrogen Evolution Reaction Research Articles

Efficient Co-MoS2 electrocatalyst for cathodic degradation of halogenated disinfection by-products in water sample

The development of non-noble metal electrocatalysts that are efficient and low-cost are being sought as alternatives to noble metals for electrochemical degradation of organic halides. In this study, Co-MoS2, a non-noble metal electrocatalyst, was synthesized and deposited on graphite felt (GF) via the hydrothermal approach. The functionalized graphite felt was used as a cathode electrode for reductive degradation of halogenated disinfection products from water samples. Five halogenated disinfection byproducts (DBPs), CHBr2Cl, C3H5Br2Cl, CHBr3, CHCl3, and CCl4 were selected as model compounds, and electro-reductive degradation by the electrode was evaluated. The batch experiments performed with an undivided electrolytic cell revealed that the Co-MoS2-GF electrode exhibited superior electrocatalytic degradation towards the DBPs compounds compared to other reported electrodes in literature. Co-MoS2-GF electrode displayed a current efficiency of ̴ 13% and degradation efficiency of more than 90% for each of the DBPs after 60 min of electrolysis. The enhanced catalytic activity of the Co-MoS2 was ascribed to the synergistic role of CoS /MoS2 towards the accelerated Volmer step of hydrogen evolution reaction (HER), which aided the production of surface-bound atomic hydrogen *H. Cyclic voltammetry and scavenging experiments clarify the formation of *H during Co-MoS2-GF catalyzed water reduction and show its contribution to DBPs degradation. The prepared Co-MoS2-GF electrode also displayed substantial stability and reusability potential even after ten cycles of recurring operation.

Enhancing hydrogen evolution reaction activity on cobalt oxide in alkaline electrolyte by doping inactive rare-earth metal

In order to reduce the energy consumption of hydrogen evolution reaction (HER), a series of lanthanum-doped cobalt oxide (x%La–Co3O4–T, where x% represents the La doping molar ratio and T represents the annealing temperature) electrocatalysts are successfully synthesized by a co-precipitation process, followed by annealing in air. Through X-ray diffraction (XRD) refinements, La3+ is doped into Co3O4 lattice, which decreases the crystallinity of Co3O4. It inhibits the aggregation and growth of Co3O4 grains. 2%La–Co3O4-350 is the optimized sample to show the lowest overpotential of 98 mV at 10 mA cm−2 with the corresponding Tafel slope of 72.8 mV dec−1 in 1 M KOH. Although La is an inactive rare-earth metal element for HER, it enhances the HER activity of Co3O4 efficiently. From further studies, the high HER catalytic activity of 2%La–Co3O4-350 can be owing to three aspects: (i) The highly dispersed and small-size Co3O4 nanoparticles caused by La doping own high specific surface area and electrochemically active surface area (ECSA), which benefits exposing more Co3+ active sites to electrolyte. (ii) La dopants make 2%La–Co3O4-350 own more oxygen vacancies that facilitating the water dissociation step of HER. (iii) La doping leads to improved conductivity and charge transfer efficiency of 2%La–Co3O4-350 during HER.

Electron density modulation of Fe1-xCoxP nanosheet arrays by iron incorporation for highly efficient water splitting

The good performance of base metal phosphides as alternative catalysts for hydrogen evolution has attracted great attention. However, phosphorus-hydrogen bonds (P-Hads) are easily formed on the surface of metal phosphides, which will severely inhibit hydrogen evolution reaction (HER). Herein, we propose a universal strategy to improve the HER activity of metal phosphides by modulating the surface electron densities. The iron modulated Fe0.29Co0.71P nanosheet arrays exhibit an overpotential of 74 mV at 10 mA cm−2 and a Tafel slope of 53.56 mV dec−1, which are close to the performance of noble metal catalysts in alkaline condition. The electronic interactions between cobalt and phosphorus are modulated after iron doping, resulting in more positively charged Co, which can promote adsorption and activation of H2O molecules and will weaken P-Hads bonds formed on the catalyst surfaces. Therefore, Fe0.29Co0.71P can optimize the adsorption and desorption of H atoms, and can promote both Volmer and Heyrovsky steps of HER. In addition, the electron density modulation of catalytic sites also improves the OER catalytic performance of Fe0.29Co0.71P. The overall water splitting electrolyzer assembled by Fe0.29Co0.71P/Ni-foam exhibits a lower cell voltage (1.59 V/10 mA cm−2), compared to that (1.61 V/10 mA cm−2) of the IrO2//Pt/C electrolyzer.

Electrocatalysis of the first electron transfer in hydrogen evolution reaction with an atomically precise CuII-organic framework catalyst

Developing atomically precise catalysts for hydrogen evolution reaction (HER) will help understand the catalytic reaction mechanisms for guiding the synthesis of new HER catalysts. A Cu-based metal-organic framework (CuII-MOF) consisting of trinuclear mixed-ligand units was prepared under hydrothermal conditions, and the structure, morphology, and elemental composition were characterized by (single crystal) XRD, TEM, SEM, XPS, BET, TGA and ATR-FTIR. Doping of 9.2 wt% CuII-MOF powder into the carbon paste electrode caused a roughly 440 mV positive shift of the HER potential at 10 mA cm−2 in 1.0 M H2SO4. The CuII-MOF showed a high working stability due to the dual-ligand-protected Cu active centers. The intrinsic catalytic mechanism was investigated by Tafel slope analysis, solid state electrochemistry and electrochemical impedance spectroscopy. The CuII ions in the CuII-MOF are successively reduced through two single-electron steps over a potential range of 0.7 to 0.1 V vs. RHE to form single-atom Cu0 active centers, on which adsorbed H atoms can be generated with a positive onset potential of about 100 mV vs. RHE through a following chemical redox reaction. The mechanistic findings point out the necessity and feasibility of developing bicomponent or bifunctional MOF-based catalysts to efficiently accelerate both the first and second electron transfer steps of HER.

Two-dimensional blue-phosphorene-phase germanium monochalcogenide photocatalysts for water splitting: From ultraviolet to visible absorption

Hydrogen generation from photocatalytic splitting of water utilizing solar energy is the most ideal way to alleviate the energy crisis at present. Using first-principles calculations, two-dimensional blue-phosphorene-phase GeX (X = S, Se) monolayers are systematically evaluated as photocatalysts for water splitting. Results show that the band edge positions of GeX locate outside the reduction potential of hydrogen and oxidation potential of water, and the values of bandgap fall into the ultraviolet range, suggesting that GeX would be served as an ultraviolet-driven photocatalyst. Interestingly, with the applying of tensile strain, the band edge positions are still suitable whereas the band gaps are significantly lowered to the visible range, and meanwhile, the intrinsic dipoles and concomitant electrostatic potential differences between Ge- and X-sides are greatly enhanced. In particular, at the 10% strain, the electrostatic potential difference reaches around 1.23 eV, which breaks the requirement of bandgap restriction for the conventional photocatalysts, thereby broadening the spectral range of light absorption from ultraviolet to visible. Using GeSe as an example, further calculations indicate that strain can enhance the optical absorption in the visible range and decrease the exciton binding energy. At the same time, the effective masses of carriers are not strongly affected by the strain. The increased internal electric field would act as an auxiliary booster to break up an exciton pair and inhibit the probability of electron-hole recombination. Moreover, strain can dramatically lower the free energy of two elementary steps of hydrogen evolution reaction. All these evidences confirm that GeX monolayers with a certain strain can serve as promising photocatalysts for water splitting under the visible range.

Boosting Electrochemical Hydrogen Evolution of Porous Metal Phosphides Nanosheets by Coating Defective TiO2 Overlayers.

Nonprecious transition metal phosphides (TMPs) have emerged as robust electrocalysts for the hydrogen evolution reaction (HER). However, the TMPs suffer from low activity for water dissociation, which greatly limits the efficiency for alkaline HER. Here, a facile yet robust strategy is reported to boost the HER of metal phosphides by coating defective TiO2 overlayers. The oxygen vacancies (Ov ) on defective TiO2 overlayers are found to possess high activity for adsorption and dissociation of water, thereby significantly promoting the initial Volmer step of HER to generate the reactive hydrogen atoms. Moreover, the porous (Co, Ni)2 P (i.e., Co2 P and Ni2 P) nanosheets provide enough active sites for adsorption and recombination of reactive hydrogen atoms to produce hydrogen gas. The catalytic synergy of (Co, Ni)2 P and Ov coupled with the hierarchically porous structure renders the porous (Co, Ni)2 P@0.1TiO2 nanosheet arrays excellent electrocatalysts for HER, showing a small overpotential (92 mV) to yield a current density of 10 mA cm-2 , a small Tafel slope (49 mV dec-1 ), and an outstanding stability. This work demonstrates a surface decoration route for enhancing the activity of nonprecious metal-based electrocatalysts for HER.

Porous Nickel-Phosphorous Electrode Synthesized By Fast-Simple Electrodeposition Process for Efficient Overall Water Splitting

Water electrolysis is an electrolysis reaction of water, and it is a technology that can produce a large amount of hydrogen environmentally friendly. The purposes of water electrolysis are responding to current hydrogen demand and storing electric energy produced from renewable energy such as solar or wind power to solve their intermittency. Water electrolysis reaction is divided into two half reactions; hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The theoretical equilibrium potential of the water electrolysis is 1.23 V, but the electrolysis reaction of the actual water requires much higher voltage due to the slow kinetics of oxygen and hydrogen reaction. Therefore, in order to increase hydrogen production efficiency, it is necessary to develop a catalyst having high activity and low cost for OER and HER. At present, transition metal based materials such as iron (Fe), cobalt (Co), and nickel (Ni) are mainly studied as high efficiency and low cost catalysts for oxygen and hydrogen evolution reactions for alkaline water electrolysis. Those transition metals are being studied in the form of various compounds such as oxide, carbide, nitride and phosphide. Among various type of compounds, transition metal phosphides (TMP) have drawn much attention for use in the alkaline water electrolysis system. These TMP catalysts have relatively good catalytic activity and stability for both OER and HER, and have high electrical conductivity compared to oxide based catalyst. In addition, TMP catalysts can be synthesized using non-toxic precursors as compared to nitride and carbide based catalysts. However, since most of TMP catalysts requires several hours to days for synthesis process, including high temperature heat treatment processes, the efficiency problem has not been solved. In this study, we have developed a method for producing nickel-phosphorus electrodes for high efficiency oxygen and hydrogen evolution reaction by fast-simple electrodeposition method. The synthesis procedure of the Ni-P electrodes ends in a few seconds at room temperature. High cathodic current density was applied to promote the generation of hydrogen bubbles and the deposition of Ni-P, thereby obtaining a highly porous structure. Hydrogen bubbles played an important role in forming the porous Ni–P layer by acting as self-dynamic templates. The surface area of highly porous Ni-P (HP Ni-P) was 50 times larger than that of the flat Ni electrode. The HP Ni-P exhibits remarkable electro-catalytic activity and stability towards the HER and OER in alkaline solutions. For the HER, overpotential at 10 mA/cm2 was 180 mV, which is slightly higher than that of Pt/C, but HP Ni-P required a lower overpotential than that of Pt/C at the high current region. For the OER, HP Ni-P shows higher catalytic activity than IrO2 at the entire current region; overpotential at 10mA/cm2 was 287 mV. The durability of HP Ni-P was also superior to the precious metal-based catalysts (Pt/C, IrO2) and Ni electrode in the long-term chronopotentiometry test. This result is ascribed to increase in surface area by hydrogen bubble generation and electronic structure change of Ni. Electronic structure change may lead to change in adsorption energy of intermediate adsorbates such as H*, OH*, O* and OOH*, which are participated in the steps of HER and OER, and can promote the kinetics of reactions in alkaline media. Figure 1

Atomistic Elucidation of Sorption Processes in Hydrogen Evolution Reaction on a van der Waals Heterostructure

Optimization of hydrogen evolution reaction (HER) on a catalytic surface is highly essential, and an atomistic elucidation of the key steps of HER in a given catalytic surface can provide better control for tuning productivity toward a hydrogen-based economy. However, the multistep nature of HER poses an important challenge in this regard and this has been further compounded in the recently developed atomic layer-based complex heterostructured HER catalysts. A multiscale approach toward this end can provide an efficient way of dissecting the likely contribution of each step. In this work, computer simulation has been used to study the first and last steps of HER on hexagonal boron nitride/graphene (hBN/G) vertical heterostructures. Using classical molecular dynamics simulation combined with enhanced sampling techniques, we atomistically map the complex hBN/G heterostructure for identifying the location of facile physical adsorption of protons on the heterostructure and facile desorption of evolved hydroge...

Design Strategies for Anode of Mg-Air Batteries and Hydrogen Evolution Reactions on Mg-RE Alloys

Mg-air battery has a theoretical energy density of 6800 Wh/kg, specific capacity of 2200 Ah/kg, and a theoretical cell voltage of 3.1 V. The values are comparable or superior to that of a conventional Li-ion battery[1]. A wide-spread use of Mg-air battery is plagued by several factors such as: (a) a low operating voltage (1.2 V) due to high polarizability of the electrodes (mixed potentials of Mg anode and air cathode), (b) low coulombic efficiency due to parasitic reactions such as hydrogen evolution, and chemical dissolution or surface layer formation, (c) sluggish oxygen reduction reaction kinetics at the air cathode. This presentation will focus on the corrosion issues of the magnesium with a particular reference to the increased hydrogen evolution with the increase in the anodic polarization, which is referred to as negative difference effect (NDE). The hydrogen evolution reaction consumes two electrons per mole of hydrogen (2H2O + 2e- → 2OH- + H2). Since the electrons required for the hydrogen evolution are supplied by the discharge reaction (Mg → Mg2+ + 2e-), the overall coulombic efficiency is drastically reduced. Therefore, the anode material for Mg-air battery should show very low catalytic activity for hydrogen evolution reaction in order to minimize the NDE. Cathodic polarization behavior of different Mg-rare earth (RE) alloys such as EV31A, WE43C, and ZE10A is being evaluated in different heat treated conditions, and different surface conditions (such as as-polished, and covered by a surface layer) along with volumetric determination of hydrogen gas evolved during cathodic and anodic polarization. The results indicate that presence of Mg(OH)2 layer helped increase the exchange current density for the hydrogen evolution reaction (HER). Enhanced hydrogen evolution on the hydroxide covered magnesium was reported by other researchers also [[2], [3]]. The Tafel slopes are steeper on the surface oxide covered specimens than the Tafel slopes of freshly polished specimens. This implies that the electrodes will be polarized significantly during the hydrogen evolution, and thus the Coulombic efficiency is reduced further. The hydrogen evolution reaction steps can be given as [[4], [5]]: Mg + H2O → Mg(OHads) (Hads) (1) which is similar to Volmer reaction. Mg(OHads) (Hads) → Mg(Oads) + H2 (2) Mg(OHads) (Hads) + H2O → Mg(OHads)2 (Hads)2 (3) Mg(OHads)2 (Hads)2 → Mg(OHads)2 + H2 (4) This presentation will focus on how the heat treatment conditions (in terms of microstructure, secondary phases, grain size), and the surface conditions influence the hydrogen evolution kinetics. The strategies to minimize the NDE and increase the performance of anode of the Mg-air battery will be discussed based on the experimental results and literature review. [1] T. Zhang, Z-.L. Tao, J. Chen, Mater. Horiz., 2014, 1, 196 [[2]] S.H. Salleh, S. Thomas, J.A. Yuwono, K. Venkatesan, N. Birbilis, Electrochim. Acta 161 (2015) 144 – 152. [[3]] G.L. Song, K.A. Unocic, Corros. Sci. 98 (2015) 758 – 765. [[4]] K.S. Williams, V. Rodriguez-Santiago, J.W. Andzelm, Electrochim. Acta 210 (2016) 261 - 270 [[5]] K.S. Williams, J.P. Labukas, V. Rodriguez-Santiago, J.W. Andzelm, Corrosion 71 (2015) 209 - 223

Efficient Hydrogen Evolution on Cu Nanodots-Decorated Ni3S2 Nanotubes by Optimizing Atomic Hydrogen Adsorption and Desorption.

Low-cost transition-metal dichalcogenides (MS2) have attracted great interest as alternative catalysts for hydrogen evolution. However, a significant challenge is the formation of sulfur-hydrogen bonds on MS2 (S-Hads), which will severely suppress hydrogen evolution reaction (HER). Here we report Cu nanodots (NDs)-decorated Ni3S2 nanotubes (NTs) supported on carbon fibers (CFs) (Cu NDs/Ni3S2 NTs-CFs) as efficient electrocatalysts for HER in alkaline media. The electronic interactions between Cu and Ni3S2 result in Cu NDs that are positively charged and can promote water adsorption and activation. Meanwhile, Ni3S2 NTs are negatively charged and can weaken S-Hads bonds formed on catalyst surfaces. Therefore, the Cu/Ni3S2 hybrids can optimize H adsorption and desorption on electrocatalysts and can promote both Volmer and Heyrovsky steps of HER. The strong interactions between Cu and Ni3S2 cause the Cu NDs/Ni3S2 NTs-CFs electrocatalysts to exhibit the outstanding HER catalytic performance with low onset potential, high catalytic activity, and excellent stability.

Alkali Cation Effect During the Oscillatory Electroreduction of H2O2 on Pt

AbstractHydrogen Peroxide Reduction Reaction (HPRR) catalyzed by Pt was studied in alkaline media and the effect of alkali cations were analyzed by the changes on dynamic instabilities presented by this system under high ohmic drop conditions. The origin of these instabilities is the competition between OH2− electroreduction and hydrogen adsorption on Pt surfaces, the latter being the first step for hydrogen evolution reaction (HER). Both HER and hydrogen adsorption are cation‐dependent which suggests that noncovalent interactions are able to stabilize the water molecules favoring the Pt−H formation. Thus, in an interphase, in which the noncovalent interactions are more effective, HPRR will proceed as an indirect poisoned system, reflecting on slow frequency oscillations (ω), for instance ωLiOH < ωNaOH < ωKOH for several H2O2 concentrations.

Nickel-based electrodes as catalysts for hydrogen evolution reaction in alkaline media

This paper reports a systematical study on the microstructures and electrochemical properties of nickel-based electrodes as low-cost catalysts for hydrogen evolution reaction (HER) in alkaline media. The electrodeposited Ni-Sn alloy displays a hydrogen overpotential of 137 mV at cathodic polarization current of 200 mA cm−2, which is lower than that of Raney-Ni and nickel net electrodes. The Tafel results show that the Volmer reaction is the rate determining step of HER for nickel net and Raney-Ni, while the hydrogen evolution reaction is controlled by a peculiar model for deposited Ni-Sn alloy. The energy consumption of alkaline water electrolysis could be reduced from 4.63 to 4.26 kW h/m3H2 by using Ni-Sn alloy electrodes to replace Raney-Ni in electrolyzers, producing good economic and environmental benefits.

Layered Noble Metal Dichalcogenides: Tailoring Electrochemical and Catalytic Properties.

Owing to the anisotropic nature, layered transition metal dichalcogenides (TMDs) have captured tremendous attention for their promising uses in a plethora of applications. Currently, bulk of the research is centered on Group 6 TMDs. Layered noble metal dichalcogenides, in particular the noble metal tellurides, belong to a subset of Group 10 TMDs, wherein the transition metal is a noble metal of either palladium or platinum. We address here a lack of contemporary knowledge on these compounds by providing a comprehensive study on the electrochemistry of layered noble metal tellurides, PdTe2 and PtTe2, and their efficiency as electrocatalysts toward the hydrogen evolution reaction (HER). Observed parallels in the electrochemical peaks of the noble metal tellurides are traced to the tellurium electrochemistry. PdTe2 and PtTe2 can be discriminated by their distinct reduction peaks in the first cathodic scans. Considering the influence of the metal component, PtTe2 outperforms PdTe2 in aspects of charge transfer and electrocatalysis. The heterogeneous electron transfer (HET) rate of PtTe2 is an order of magnitude faster than PdTe2, and a lower HER overpotential of 0.54 V versus reversible hydrogen electrode (RHE) at a current density of -10 mA cm-2 is evident in PtTe2. On PdTe2 and PtTe2 surfaces, adsorption via the Volmer process has been identified as the limiting step for HER. A general phenomenon for the noble metal tellurides is that faster HET rates are observed upon electrochemical reductive pretreatment, whereas slower HET rates occur when the noble metal tellurides are oxidized during pretreatment. PtTe2 becomes successfully activated for HER when subject to oxidative treatment, whereas oxidized or reduced PdTe2 shows a deactivated HER performance. These findings provide fundamental insights that are pivotal to advancing the field of the underemphasized TMDs. Furthermore, electrochemical tuning as a means to tailor specific properties of the TMDs is advantageous for the development of their future applications.

Hierarchical Integration of Photosensitizing Metal-Organic Frameworks and Nickel-Containing Polyoxometalates for Efficient Visible-Light-Driven Hydrogen Evolution.

Metal-organic frameworks (MOFs) provide a tunable platform for hierarchically integrating multiple components to effect synergistic functions that cannot be achieved in solution. Here we report the encapsulation of a Ni-containing polyoxometalate (POM) [Ni4 (H2 O)2 (PW9 O34 )2 ](10-) (Ni4 P2 ) into two highly stable and porous phosphorescent MOFs. The proximity of Ni4 P2 to multiple photosensitizers in Ni4 P2 @MOF allows for facile multi-electron transfer to enable efficient visible-light-driven hydrogen evolution reaction (HER) with turnover numbers as high as 1476. Photophysical and electrochemical studies established the oxidative quenching of the excited photosensitizer by Ni4 P2 as the initiating step of HER and explained the drastic catalytic activity difference of the two POM@MOFs. Our work shows that POM@MOF assemblies not only provide a tunable platform for designing highly effective photocatalytic HER catalysts but also facilitate detailed mechanistic understanding of HER processes.

Hierarchical Integration of Photosensitizing Metal–Organic Frameworks and Nickel‐Containing Polyoxometalates for Efficient Visible‐Light‐Driven Hydrogen Evolution

AbstractMetal–organic frameworks (MOFs) provide a tunable platform for hierarchically integrating multiple components to effect synergistic functions that cannot be achieved in solution. Here we report the encapsulation of a Ni‐containing polyoxometalate (POM) [Ni4(H2O)2(PW9O34)2]10− (Ni4P2) into two highly stable and porous phosphorescent MOFs. The proximity of Ni4P2 to multiple photosensitizers in Ni4P2@MOF allows for facile multi‐electron transfer to enable efficient visible‐light‐driven hydrogen evolution reaction (HER) with turnover numbers as high as 1476. Photophysical and electrochemical studies established the oxidative quenching of the excited photosensitizer by Ni4P2 as the initiating step of HER and explained the drastic catalytic activity difference of the two POM@MOFs. Our work shows that POM@MOF assemblies not only provide a tunable platform for designing highly effective photocatalytic HER catalysts but also facilitate detailed mechanistic understanding of HER processes.

The inhibition effect of SeO2 on hydrogen evolution reaction in MnSO4–(NH4)2SO4 solution

The hydrogen evolution reaction (HER) on the stainless steel electrode in MnSO4–(NH4)2SO4 solution (MA solution) with and without SeO2 was studied by the linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS) and chronoamperometry. It was found that SeO2 could effectively inhibit HER, but the control step of HER was not changed. The apparent activation energy of HER was increased from 50.56 kJ mol−1 to 58.83 kJ mol−1 after adding 9.0 × 10−4 mol L−1 SeO2. The charge transfer resistance of HER was also increased. The inhibitory process of SeO2 on HER could be explained as follows: Se (IV) was reduced to Se (0), the morphology and composition of electrode surface were changed evidently by the deposition of selenium. The results of SEM and XRD further indicate that the explanation of inhibitory process of SeO2 on HER in MA solution is reasonable.

Ab Initio Electrochemistry: Exploring the Hydrogen Evolution Reaction on Carbon Nanotubes

Density functional theory (DFT) was employed to investigate the hydrogen evolution reaction (HER) on pristine and nitrogen-doped carbon nanotubes (CNTs) in acidic solution. As the reaction is an electrocatalytic surface reaction, an accurate description of HER requires performing simulations under constant electrode potential conditions. To this end, we examined HER at several electrode charges allowing us to determine grand canonical activation energies as a continuous function of electrode potential. By studying the elementary steps of HER—the Volmer, Tafel, and Heyrovsky reactions—and by considering hydrogen coverage effects, we found that the Volmer–Heyrovsky mechanism is the predominant HER mechanism on CNTs with the Heyrovsky step being rate-determining. Our results indicated that CNTs are electrochemically active toward HER, which is seen as a decrease in activation energies with growing electrode potential, but that the activity is lower than on platinum matching experimental data. Substitutional ...

Electrodeposited Pd-Ni-Mo film as a cathode material for hydrogen evolution reaction

A Pd-Ni-Mo film was prepared on stainless steel substrate as a novel electrode material for hydrogen evolution reaction catalysis. The surface micro-morphology, chemical composition and microstructure of the Pd-Ni-Mo film were characterizated with SEM, EDS, XPS and TEM. The obtained film is a multiple phase ternary alloy containing crystallines and amorphous phases. The electrochemical measurements showed that the Pd-Ni-Mo film has excellent catalytic activity for hydrogen evolution reaction with good corrosion resistance in 1M NaOH solution. The proton discharge electrosorption is the rate determining step of hydrogen evolution reaction on Pd-Ni-Mo film surface. The better electrocatalysis performance of the Pd-Ni-Mo film is attributed to its larger real surface as well as the enhanced electrochemical activity of the film surface due to the alloying effect.

Effect of Cerium on Gas Evolution Behavior of Pb-Ca-Sn Alloy

The effect of Ce on the behavior of gas evolution on Pb-Ca-Sn alloy in 4.5 mol * L −1 H 2SO 4 was investigated using cyclic voltammetry (CV), cathodic polarization curves and AC impedance (EIS). Cyclic voltammetry experiments show that the current of oxygen evolution on Pb-Ca-Sn-Ce electrode is lower than that of Pb-Ca-Sn electrode in the same anodic voltage. Moreover, the oxygen evolution potential on the former electrode is greater than that on the latter, and this means that Ce can increase the potential of oxygen evolution on Pb-Ca-Sn alloy. The AC impedance experiments show that Ce can also enhance the resistance of hydrogen evolution on Pb-Ca-Sn electrode, i.e., Ce can inhibit the hydrogen evolution on Pb-Ca-Sn electrode. The reason why Ce decreases the volume of hydrogen evolution on Pb-Ca-Sn alloy is that Ce increases the resistance of absorbing step of hydrogen evolution reaction. All the experimental results indicate that Pb-Ca-Sn-Ce alloy can rapidly decrease the oxygen and hydrogen evolution on Pb-Ca-Sn-Ce alloy. It is concluded that Pb-Ca-Sn-Ce alloy can promote the maintenance-free property of lead acid battery, and can serve as the candidate of the grid material for maintenance-free lead acid battery.

Components of overvoltage of hydrogen electrode reaction on nickel

For the case of hydrogen evolution reaction (HER) in alkaline solutions on nickel, the overvoltage of the electron transfer step (the first step of HER) was separated from that of the overall reaction on the basis of the results obtained by the galvanostatic transient method, which has been developed by us earlier. The difference of the overall-reaction overvoltage and electron-transfer overvoltage, which is considered as the overvoltage of the step of an adsorbed hydrogen atom recombination (the last step of HER), was also determined. It is known that on nickel, during cathodic polarization in alkaline solutions, the intermetallic compound M(I) of an alkali metal with nickel is formed as practically the main intermediate. In this case, the Tafel line, corresponding to the last step, shows a slope of 70–80 mV, and the observed overvoltage can be explained in terms of the decrease of the work function of the surface component, caused by the M(I) formation. On the other hand, on a cobalt-deposit-modified nickel, the Tafel line shows a slope of 30 mV, even in alkaline solutions. The nickel surface may be completely covered with the cobalt deposit. Therefore, no intermetallic compound seems to be formed on the surface, and the main intermediate is likely to be an adsorbed hydrogen atom, as in the case of HER on platinum in acid solutions.