Hydrogen Evolution Overpotential Research Articles

Crafty design of chemical bonding to construct MoO2/CdS nanorod photocatalysts for boosting hydrogen evolution

An efficient MoO2/CdS photocatalyst has been successfully constructed by a relatively facile way to construct a specific combination mode through chemical bond, which results in strong interaction between MoO2 nanoparticles and CdS nanorods. X-ray photoelectron spectroscopy further confirms the formation of Mo–S bonding, which acts as a connection bridge and develops an intimate contact between CdS-NRs and MoO2 nanoparticles. Benefitting from the synergic effect of the enhancement on the light absorption, carriers’ efficient separation and lower the overpotential of hydrogen evolution, the obtained MoO2/CdS composite has shown an excellent enhancement in photocatalytic H2 generation and the optimal H2 evolution rate reaches as high as 30 times than that of pure CdS nanorods. We have experimentally shed light on the mechanism of this excellent enhancement performance in detail. Moreover, our work can broaden the construction and the application of developing other efficient photocatalytic material containing transition metal oxide.

FexNiyOOH/etched stainless steel mesh with different morphology for water electrolysis

Water electrolysis was recognized as an effective method for new energy sources. In this work, an effective FexNiyOOH/ESS with high surface area and good catalytic activity was prepared for water electrolysis. Its morphologies at different ratio of Fe/Ni atoms were diverse, such as flower ball, flake, and block, etc. Test results showed that at 10 mA cm−2 and 300 mA cm−2, the hydrogen evolution overpotentials of Fe1.5Ni0.5OOH/ESS were 172 mV and 258 mV. The oxygen evolution overpotentials of Fe0.2Ni1.8OOH/ESS were 208 mV and 308 mV at 10 mA cm−2 and 600 mA cm−2. During the 136-h stability test, the oxygen evolution activity of Fe0.2Ni1.8OOH/ESS was basically unchanged. The Fe1.5Ni0.5OOH//Fe0.2Ni1.8OOH in alkaline conditions presented good performance for water electrolysis. Water electrolysis experiment was carried out at 1.58 V, and the current density reached to 10 mA cm−2. FexNiyOOH/ESS exhibited higher electrocatalytic activity and superior stability at high current density.

Zinc anode with artificial solid electrolyte interface for dendrite-free Ni-Zn secondary battery

Rechargeable nickel-zinc battery is regarded as a prospective choice for next-generation energy storage device due to its good safety, environmental friendliness and high energy density. However, zinc anode inevitably suffers from uncontrollable growth of zinc dendrites and the dissolution of zinc metal in high-concentration alkaline electrolytes, resulting in poor cycle stability and severely hampering the widespread applications of nickel-zinc batteries. Herein, a unique zinc anode with artificial solid electrolyte interface (ASEI) is facilely constructed via the rolling-tearing of tin and zinc foils and subsequent surface-based chemical reaction in a lead salt solution. The as-prepared ASEI composed of lead film has an efficient protective effect on preventing the dissolution of zinc anode. Meanwhile, the lead element and residual tin can not only enhance hydrogen evolution over-potential of zinc anode but affect the zinc growth mechanism. As a consequence, an excellent cyclic performances upto 100 cycles (capacity retention: 90%) with high reversible capacities are achieved for the zinc anode with AESI.

V2O5 nanopaper as a cathode material with high capacity and long cycle life for rechargeable aqueous zinc-ion battery

Aqueous batteries are suitable for large scale energy storage due to cost and safety concerns. Among all aqueous batteries, rechargeable aqueous zinc-ion battery is a promising choice because zinc electrode has low equilibrium potential, high exchange current density, and high hydrogen evolution overpotential. However, since zinc ion is a divalent cation, it is difficult to find a cathode material in which zinc ion can reversibly insert and extract. In this work, we introduce a novel V2O5 nanopaper consisting of V2O5 nanofibers and carbon nanotubes as reversible Zn-ion cathode. V2O5 has a layered crystalline structure. The spaces between the oxide layers may serve as 2-dimensional diffusion pathways for Zn ions. Meanwhile, the nanofiber morphology endows the material with short ionic diffusion distance and may tolerate high volume change. As a result, the V2O5 nanopaper cathode delivers a high capacity of 375 mAh g−1 and long cycle life up to 500 cycles.

New porous bismuth electrode material with high surface area

Bismuth electrodes are particularly interesting owing to their high hydrogen evolution overpotential and electrocatalytic activity. In this work, a novel porous bismuth electrode was prepared via an electrochemical deposition of bismuth on a porous graphite felt of high specific surface area, employing bismuth(III) oxide as reactant and a flow electrochemical cell as reactor. A solubility up to 1molL−1 of bismuth was obtained in basic medium using a suitable complexing agent. We solved the problems linked to the heterogeneous potential distribution in the 3D porous structure and to the formation of dendritic excrescences that led to mechanically fragile material by using a suitable flow electrochemical cell, a periodically changing current with short on-pulses and long off-pulses and by limiting the electrodeposition of Bi on the external surfaces of the felt due to diffusion. A Bi-modified electrode with high specific surface area and low bulk density was achieved using this method.

PECULIARITIES OF ELECTRODEPOSITION OF COBALT—WOLFRAM—RENIUM ALLOY

The methods of stationary voltammetry and chronovoltammetry have been used to study deposition processes of ternary CoWRe alloys at different rhenium content of the electrolyte and deposition current density. It has been found that the limiting currents have a diffusive nature and are proportional to the concentration of perrhenate ions in the electrolyte. The CoWRe alloys should be formed by the discharge of bimetallic citrate complexes of the following composition [(Co)(WO4)(H)(Cit)]2- and rhenium electrodeposition. Rhenium does not form complexes with citrate ions and deposits better in an alloy with iron group metals than in the form of an individual metal from a perrhenate solution. It can be assumed that the discharge of rhenium into the alloy occurs from a surface complex, the nature of which has not yet been established. The alloy current efficiency reaches 93% due to the high overpotential of hydrogen evolution on the alloy surface. According to the results of investigations of the catalytic properties of alloys in the hydrogen reduction reaction, it has been found that with increasing the rhenium content of the electrolyte and alloy, an increase in hydrogen overpotential is observed. Based on the Tafel coefficients found, it was found that in an acidic and neutral medium, the limiting stage of the cathodic and anodic reaction is the transfer of the first electron. In an alkaline medium, the anode process is complicated by the simultaneous transport of two electrons. The found values of corrosion resistance are 1-2 kOm·cm-2 in solutions of 0.01 M H2SO4; 20-110 kOm·cm-2 in 2.5% NaCl; 10-30 kOm·cm-2 in 1.0 M KOH. Based on the dependence of corrosion resistance on the refractory metals content of the alloy and the electrodeposition conditions, the optimum deposition current density of 10 mA·cm-2 has been found.

Chalcogenide vacancies drive the electrocatalytic performance of rhenium dichalcogenides.

The hydrogen evolution reaction (HER) is one of the most promising ways to produce clean energy. However, its wide-spread use is hindered by the price of the state-of-the-art catalysts based on precious metals. Transition metal dichalcogenide (TMD) nanomaterials are a cheap alternative, but a relatively large portion of them remains unexplored in terms of the HER. Here we report the HER performance of rhenium disulfide and diselenide in an acidic environment. We used sodium naphthalenide as an exfoliation agent. In comparison with other TMDs, the degree of exfoliation was relatively low. On the other hand, rhenium disulfide and diselenide both exhibit high chemical stability towards oxidation even after the exfoliation. The reported HER performance of the exfoliated rhenium dichalcogenides was strongly dependent on electrochemical treatment and to further enhance the performance, we used a series of electrochemical pretreatments at potentials as high as -2 V in sulfuric acid. While the morphology of the samples remained unchanged, the surface was found out to be chalcogen deficient, pointing out the formation of chalcogen vacancies. Consequentially, the HER performance was substantially enhanced. These results were corroborated by theoretical calculations showing improved bonding of hydrogen by chalcogenide vacancies at the surface. Our results show that a very simple electrochemical procedure can be used to improve the electrocatalytic performance of rhenium dichalcogenides and, possibly, also other TMDs.

Hydrogen production by photocatalytic water splitting of aqueous hydrogen iodide over Pt/alkali metal tantalates

Reduction of the hydrogen evolution overpotential and durability in aqueous HI are important factors for the cocatalyst loaded onto KTaO3.

Electrochemical Preparation and Post-treatment of Composite Porous Foam NiZn Alloy Electrodes with High Activity for Hydrogen Evolution

Composite porous foam NiZn alloy electrodes with nano pore structure were prepared by the combination of eletrodeposition, heat treatment and HCl etching. The morphology of the electrodes was examined by scanning electron microscopy (SEM). And the component of the electrodes was analyzed by Energy Dispersive Spectrum (EDS). The specific surface area and pore size of the electrode were investigated by nitrogen adsorption. The phase constituents were analyzed by X ray diffraction (XRD), and the electrocatalytic characteristics for hydrogen evolution reaction of the electrodes in 30% (mass fraction) KOH solution were investigated by cathode polarization curve. The experimental results showed that the pores were formed on surface of the foam NiZn alloy electrodes after heat treatment at 600 °C, and with the etching by 10% HCl, nano layered structure was formed on the surface of the porous skeleton. Compared with the nickel foam, the surface area of the NiZn foam alloy electrode became larger, and the nano pore structure had good catalytic activity. At current density of 200 mA·dm−2, the hydrogen evolution overpotential of the NiZn foam alloy electrodes were reduced by 222 mV and 276 mV, respectively, through heat treatment of 600 °C and etching in 10% HCl solution, which indicated that the hydrogen evolution overpotential was effectively reduced because of the composite nano porous structure, while the activity of hydrogen evolution of the electrodes was obviously improved.

Improved hydrogen recovery in microbial electrolysis cells using intermittent energy input

Microbial electrolysis cell (MEC) is a bioelectrochemical technology that can produce hydrogen gas from various organic waste/wastewater. Extra voltage supply (>0.2 V) is required to overcome cathode overpotential for hydrogen evolution. In order to make MEC system more sustainable and practicable, it is necessary to minimize the external energy input or to develop other alternative energy sources. In this study, we aimed to improve the energy efficiency by intermittent energy supply to MECs (setting anode potential = −0.2 V). The overall gas production was increased up to ∼40% with intermittent energy input (on/off = 60/15sec) compared to control reactor. Cathodic hydrogen recovery was also increased from 62% for control MEC to 69–80% for intermittent voltage application. Energy efficiency was increased by 14–20% with intermittent energy input. These results show that intermittent voltage application is very effective not only for energy efficiency/recovery but also for hydrogen production as compared with continuous voltage application.

Tin Alloy Nanoparticles for Selective Electrocatalytic Reduction of Carbon Dioxide to Formate

The selective electrocatalytic reduction of CO2 to formate ions or to formic acid is attracting the attention of several researchers. This is mainly because these products can be utilized as hydrogen carriers and as fuels for direct or for indirect fuel cells. In aqueous media, electrocatalysts formed by metals with high hydrogen evolution overpotential, such as Pd, Hg, In, and Sn, are selective for the production of formate (or formic acid, depending on the electrolyte pH). Among these metals, Sn has gained notice because it is abundant and relatively nontoxic. The reasons for the selectivity observed on Sn electrodes are still in debate and has been the subject of recent papers [1,2]. It seems that tin allows the carbon dioxide reduction intermediate to be adsorbed via the oxygen atoms after a proton-couple electron transfer step, so conducting the reaction to the production of formate. In addition, the studies have been discussed the effect of the surface hydroxides, which may enhance the CO2 reduction mainly via two effects: (i) suppressing or decelerating the water electro-reduction and; (ii) allowing a first chemical reaction step with CO2, so producing an adsorbed bicarbonate intermediate (via oxygen atoms), so facilitating the protonation of the carbon atom. In this paper, we will present some results obtained for the CO2 electrochemical reduction on nanostructured tin-alloys, such as Sn-Pd and Sn-Co. The faradaic efficiencies for formate (or formic acid) production were determined via quantitative determination by cyclic voltammetry and experiments of on-line Differential Electrochemical Mass Spectrometry (DEMS) for the formate electro-oxidation after experiments of CO2 electrolysis. It will be discussed the correlation between the nanostructure morphology and Sn oxidation state with the stability and faradaic efficiency for the production of formate (or formic acid) on different electrolytes and pHs. We expect that the obtained results will serve to further understand the main electrocatalyst features that control the selectivity and stability for the CO2 reduction to formate. [1] J.T. Feaster, C. Shi, E.R. Cave, T. Hatsukade, D.N. Abram, K.P. Kuhl, C. Hahn, J.K. Norskov, T.F. Jaramillo, ACS Catal. 7 (2017) 4822 – 4827. [2] J.E. Pander, M.F. Baruch, A.B. Bocarsly, ACS Catal. 2016, 6, 7824−7833. Acknowledgements The authors gratefully acknowledge financial support from FAPESP (2016/13323-0 and 2013/16930-7) and CNPq (306469/20162).

Non-noble metal Cu as a cocatalyst on TiO2 nanorod for highly efficient photocatalytic hydrogen production

Nanorod-like TiO2 photocatalysts with controllable particle size for hydrogen production were synthesized based on H2Ti3O7 precursors using hydrothermal and ion exchange methods. The characteristics of TiO2 photocatalysts, such as morphology, specific areas and crystalline quality, can be adjusted by changing hydrothermal conditions, thus optimizing its photocatalytic activity for hydrogen evolution. The TiO2 nanorod possesses the highest photocatalytic activity, even higher than P25, when the hydrothermal temperature is 140 °C, which should be ascribed to its large specific area and good crystalline quality. Non-noble metal Cu as a substitute of Pt was loaded on the surface of TiO2 nanorod to promote the photocatalytic hydrogen production. It was confirmed that, during the photocatalytic reaction process, Cu0 rather than CuOx acted as active sites to enhance the photocatalytic activity. The highest photocatalytic H2 evolution rate of Cu/TiO2 reaches 1023.8 μmol·h−1 when the amount of loading is 0.1 wt%, reaching the 20 times of that of bare TiO2 (49.4 μmol·h−1) and approaching that of Pt/TiO2 (1161.7 μmol·h−1). Non-noble metal Cu not only facilitated the separation of carriers, but reduced the overpotential of hydrogen evolution, thus promoting the photocatalytic activity for hydrogen production.

Sodium hexa meta phosphate impact as electrolyte additive on electrochemical behavior of lead-acid battery

Sodium hexa meta phosphate (SHMP) is an inorganic salt with a polymeric structure which produces massive branches of hexa meta phosphate anions (HMP−) in an acidic environment. The main goal of the presented work is to investigate the influence of SHMP as an electrolyte additive on the performance of the lead-acid batteries. To achieve the point, the examinations are done in two separate ways: i) Investigation electrochemical behavior of lead alloy electrode, by studying Hydrogen and Oxygen Evolution Reaction (HER and OER) with electrochemical techniques including; Cyclic Voltammetry and Linear Sweep Voltammetry. Then, Scan of Electron Microscopy (SEM performed to study the surface of the electrode after electrochemical treatments. By increasing SHMP concentration, overpotential of hydrogen and oxygen evolution is increased due to improving particle size of PbSO4 which consequently lessens water loss. ii) Real battery tests including; water consumption test, capacity measurements and High Rate Partial State of Charge (HRPSoC) as a cycle-life examination. Also, Scan of Electron Microscopy from the surface of the negative electrode and X-Ray Diffraction (XRD) analysis of negative electrode plate at the charge and discharge state after cycle-life test are prepared for study the PbSO4 particles size and quantity or the morphology of sulfating layer. Addition of SHMP to the electrolyte of the lead-acid battery increases cycle-life numbers and accordingly prolongs battery life. Therefore, SHMP is a promising electrolyte additive and it would be used with a combination of additives to increase the overall performance of a lead-acid battery.

In situ photodeposition of cobalt on CdS nanorod for promoting photocatalytic hydrogen production under visible light irradiation

Non-noble metal Co were loaded on CdS for enhancing photocatalytic activity of water splitting by a simple and efficient in situ photodeposition method. The Co particles with diameter ca. 5 nm were photoreduced and then loaded on the surface of CdS. The loading of Co can not only effectively promote the separation of electrons and holes photoexcited by CdS, but reduce the overpotential of hydrogen evolution as well, thus enhancing photocatalytic activity of water splitting. The highest photocatalytic H2 evolution rate of Co/CdS reaches up to 1299 μmol h−1 under visible light irradiation(λ > 420 nm) when the amount of loading is 1.0 wt%, which is 17 times of that of pure CdS and achieves 80% of that of 0.5 wt%Pt/CdS. This work not only exhibits a pathway to obtain photocatalysts with high photocatalytic activity for hydrogen production, but provides a possibility for the utilization of low cost Co as a substitute for noble metals in photocatalytic hydrogen production.

Selective Electrochemical Reduction of Carbon Dioxide to Ethanol on a Boron- and Nitrogen-Co-doped Nanodiamond.

Electrochemical reduction of CO2 to ethanol, a clean and renewable liquid fuel with high heating value, is an attractive strategy for global warming mitigation and resource utilization. However, converting CO2 to ethanol remains great challenge due to the low activity, poor product selectivity and stability of electrocatalysts. Here, the B- and N-co-doped nanodiamond (BND) was reported as an efficient and stable electrode for selective reduction of CO2 to ethanol. Good ethanol selectivity was achieved on the BND with high Faradaic efficiency of 93.2 % (-1.0 V vs. RHE), which overcame the limitation of low selectivity for multicarbon or high heating value fuels. Its superior performance was mainly originated from the synergistic effect of B and N co-doping, high N content and overpotential for hydrogen evolution. The possible pathway for CO2 reduction revealed by DFT computation was CO2 →*COOH→*CO→*COCO→*COCH2 OH→*CH2 OCH2 OH→CH3 CH2 OH.

Hydrogen evolution during the electrodeposition of gold nanoparticles at Si(100) photoelectrodes impairs the analysis of current-time transients

The electrodeposition of noble metals, particularly gold, on semiconducting surfaces is a common step in the development of optoelectronic and catalytic devices. Theoretical models of electrodeposition transients can provide mechanistic insights on nucleation and growth of metal particles. Here we study to what extent these models can be applied to the growth of gold nanoparticles on semiconductor photoelectrodes, with the ultimate purpose of being able to control in two dimensions the electrodepostion process. We have examined current transients for the reduction of aurate salts at Si(100) photocathodes and have made adjustments both to the experimental parameters as well as to the available models so as to account for parallel adsorption steps. We have observed to what extent these models hold predictive power for a nucleation process on semiconducting photoelectrodes. We found that the hydrogen evolution reaction is significant even at very basic pH values, leading to a poor match between the modelled and actual outcomes in electrodeposition experiments. We have concluded that the catalytic activity of gold particles and semiconductor photoeffects make it difficult to rely on current transients alone to refine the experimental conditions for the growth of gold particles on Si(100) photocathodes. Specifically, it is proposed that hydrogen evolution causes turbulence leading to the displacement of particles and significant aggregation on the surface. A solution to this problem is to electrodeposit metals with high overpotentials for hydrogen evolution, such as copper, which allows us to control nucleation and ultimately to use illumination patterns to spatially address nanoparticle deposition on semiconducting surfaces.

Influence of the Oxide Content in the Catalytic Power of Raney Nickel in Hydrogen Generation

ABSTRACTThe influence of oxides in the hydrogen evolution on Raney nickel electrocatalysts was characterized by electrochemical impedance measurements. In addition, these materials show competitive overpotentials for hydrogen evolution with a modified Watts bath as a binder for the Raney nickel. The optimum result was −190 mV of overpotential at 100 mA cm−2. Oxygen in the Raney Ni catalyst affects its electroactivity toward hydrogen evolution. The source of oxygen is related to the presence of chloride ions in the modified Watts bath. A Watts bath binds Raney Ni particles to the surface of the catalysts and chloride regulates the oxygen content in the nickel binder during electrodeposition. High oxygen content increases the hydrogen evolution overpotential of the electrode. The electroactivity of the synthesized porous coatings was evaluated by polarization curves and impedance plots. In addition, surface characterization by X-ray diffraction, field emission–scanning electron microscopy equipped with energy-dispersive analysis, and X-ray photoelectron spectroscopy is reported.

Electroreduction of Carbon Dioxide to Formic Acid and Methanol over a Palladium/Polyaniline Catalyst in Acidic Solution: A Study of the Palladium Size Effect

AbstractWe controlled the reaction temperature and feeding rate of the reducing agent to show that Pd nanoparticles (NPs) with different sizes can be synthesized from the reduction of their precursor on polyaniline (PANI) as a solid support. We used UV/Vis spectroscopy, 1H NMR spectroscopy, and IR spectroscopy to identify the electronic and catalytic interactions between Pd NPs and PANI. For the first time, that the unique redox properties of Pd/PANI display a high overpotential for hydrogen evolution, which suppresses this competitive reaction for the electroreduction of CO2 in an acidic solution. As a result, two main liquid products (HCOOH and CH3OH) can be produced selectively with only trace amounts of CO in the gas phase. The current efficiencies for HCOOH and CH3OH increase with the decreasing Pd NP size within the potential range of −0.5 to −0.9 V. The highest current efficiencies for HCOOH (22.8 %) and CH3OH (5.4 %) are thus obtained over Pd(1.31 nm)/PANI at −0.9 V.

(Invited) Engineering Surface Structures and Energetics of α-Fe2O3 and p-Si for Efficient Solar Water Splitting

Solar hydrogen conversion via photoelectrochemical water splitting is an important technology for energy and environment sustainability. Since the pioneering work of Fujishima and Honda in 1972, tremendous research on semiconductor-based photoelectrochemical water splitting has yielded better understanding of the processes as well as encouraging development of high efficiency photoelectrodes for solar hydrogen generation. In this talk, some recent progresses in heterostructures of α-Fe2O3and p-Si for photoelectrochemical solar water splitting in our group will be introduced. Given the narrow band gap enabling excellent optical absorption, increased charge carrier density and accelerated surface oxidation reaction kinetics become the key points for improved photoelectrochemical performances for water splitting over α-Fe2O3 photoanodes. By engineering the surface structures of α-Fe2O3 nanorods with AgxFe2-xO3, TiO2 and HfO2overlayers, the surface charge recombination was greatly inhibited and the surface water oxidation kinetics were efficiently accelerated, resulting in remarkable enhancement in PEC water splitting performances. p-Si has captured intensive attentions for solar hydrogen conversion due to its high natural abundance and narrow band gap (~1.1 eV). However, the slow charge-transfer kinetics at the p-Si/electrolyte interface lead to large overpotentials for hydrogen evolution and electrocatalysts are always necessary. Recently, we successfully engineered the surface energetics of p-Si with n-WO3 overlayer and Ni molecular complexes, which gave rise to a great anodic shift of up to 300 mV in onset potential for photocathodic water reduction.

Porous Functionalized Self-Standing Carbon Fiber Paper Electrodes for High-Performance Capacitive Energy Storage.

A facile and cost-efficient approach to functionalize raw carbon fiber paper (CFP) used for a self-standing capacitive electrode has been proposed here. Benefiting from the improved specific surface area and surface functional groups, the functionalized CFP (F-CFP) showed much enhanced capacitive performance, 3 orders of magnitude higher than that of the raw CFP. It delivered the areal capacitance of 1275 mF cm-2 at 5 mA cm-2 with a rather wide voltage window of 1.4 V (-0.4 to 1 V vs Ag/AgCl) in 0.5 M H2SO4. However, in a neutral 1 M Na2SO4 aqueous solution, although the areal capacitance of 1115 mF cm-2 at 3 mA cm-2 is slightly smaller, the potential window is much wider (2 V, -1 to 1 V vs Ag/AgCl), indicating a high overpotential of hydrogen evolution. The areal capacitance was still as high as 722 mF cm-2 at a very fast charge-discharge current density of 50 mA cm-2, and about 66% of the initial capacitance (at 3 mA cm-2) was remained in Na2SO4, indicating considerable rate capability.