Highly efficient electrocatalytic hydrogen production via MoSx/3D-graphene as hybrid electrode

Molybdenum sulfide (MoS_x) has recently emerged as a promising catalyst for the hydrogen evolution reaction (HER) in water splitting that may replace the noble metal, such as platinum, as a cost-effective and high catalytic materials. It has been reported that two-dimensional structured MoS_x exhibit significant amount of exposed S-edge, which can be an active electrocatalytic catalyst for hydrogen production. However, the current reports mainly focusing on the planar electrode, where the catalyst utilization and the number of active sites are limited due to the lower exposed specific surface area (SSA) of supporting electrodes. In this work, we utilize the freeze-drying method to produce a porous three-dimensional (3D) structure assembled by graphene flakes. The as-prepared 3D graphene scaffold shows high surface area, high porosity while low density, which makes it as an ideal conductive electrode for supporting of MoS_x catalysts. Moreover, it was found out that the crystallinity of MoS_x, controlled by thermolysis temperature of thiosalts precursor ((NH₄)₂MoS₄), shows significantly influence the performance of HER. The optimized annealing temperature for the designed hybrid electrodes (MoS_x/3D-graphene) was found to create a lot of active sites, which facilitate the electrocatalytic performance for water splitting (overpotential of 163 mV @10 mA/cm² and a Tafel slope of 41 mV/dec). The study provides a potential material, which could pave the way for future applications of hydrogen energy.     

A novel hazelnutt bagasse based activated carbon as sodium borohydride methanolysis and electrooxidation catalyst

In this study, activated carbon is produced from defatted hazelnut bagasse at different activation conditions. The catalytic activities of activated carbons are evaluated for NaBH₄ methanolysis and electrooxidation. These materials are characterized by N₂ adsorption-desorption, FTIR, SEM-EDS and XPS and results show that these materials are prepared successfully. N₂ adsorption-desorption results reveal that activated carbon (FH3-500) has the highest BET surface area as 548 m²/g, total pore volume as 0.367 cm³/g and micropore volume as 0.205 cm³/g. On the orher hand, as a result of hydrogen production studies, FH3-500 activated carbon catalyst has the highest initial hydrogen production rate compared to other materials. At 50 °C, this metal-free activated carbon catalyst has a high initial hydrogen production rate of 13591.20 mL/min.g_cat, which is higher than literature values. Sodium borohydride electrooxidation measurements reveal that FH2-500 also has the highest electrocatalytic activity and stability. Hazelnut pulp-based activated carbons are firstly used as a metal-free catalyst in the methanolysis and electrooxidation of sodium borohydride, and its catalytic activity is good as a metal-free catalyst. The results show that the hazelnut pulp-based activated carbon catalyst is promising as a metal-free catalyst for the methanolysis and electrooxidation of sodium borohydride.     

Characterization of the Ni-Mo catalyst formed in situ during hydrogen generation from alkaline water electrolysis

Objective of this work was to investigate the electrocatalytic efficiency using quasi-potentiostatic, galvanostatic and impedance spectroscopy techniques of the Ni-Mo catalysts obtained by in situ electrodeposition in an alkaline, 6 M KOH, electrolyser. In accordance to our previous studies, synergetic effect is observed, with its maximum at industrial conditions (high temperature and current density). The Tafel slopes are around 120 mV and exchange current densities are close to 10⁻² mA cm⁻² (three orders of magnitude higher compared to the bulk Ni). Moreover, formed deposit possess high stability during prolonged electrolysis. Results are presented to show the Tafel slopes, the exchange current densities, the apparent energy of activation, the apparent electrochemical surface and the stability of in situ formed Ni-Mo catalyst. Results suggest to significant catalytic performance not only from the increase of the real surface area of electrodes, but also from the true catalytic effect.     

Self-supported three-dimensional WP2 (WP) nanosheet arrays for efficient electrocatalytic hydrogen evolution

The development of highly efficient, stable, eco-friendly and low-cost noble-metal-free electrocatalysts is still a great challenge to generate large scale hydrogen fuel from water. In this concern, self-supported WP₂ and WP nanosheet (NS) arrays were prepared through an in-situ solid-phase phosphidation of WO₃ nanosheet arrays on carbon cloth (CC), whereas, different phosphating temperatures of 650 °C, 800 °C for 2 h, has been utilized to attain different WP₂ NS/CC, WP NS/CC catalysts. Remarkably, the electrocatalysts of WP₂ and WP NS arrays exhibit an outstanding hydrogen evolution (HER) performance in acidic environment, with a low overpotential of 140 mV and 175 mV at 10 mA cm⁻², a Tafel slope of 85 mV dec⁻¹ and 103 mV dec⁻¹, respectively. Furthermore, Density Functional Theory (DFT) calculations reveal that the enhanced HER activity of WP₂ catalyst is attributed to the lowered hydrogen adsorption free energy on WP₂ surface, which is much lesser than that on the WP catalyst surface. As a result, WP₂ exhibit superior intrinsic catalytic activity than WP. This study offers a valuable way for the synthesis of highly efficient three-dimensional self-supporting catalytic electrodes, and beneficial for realizing the intrinsic electrocatalytic properties of tungsten phosphide for improved water splitting reactions.     

Highly active porous Co–B nanoalloy synthesized on liquid-gas interface for hydrolysis of sodium borohydride

Porous Co–B nanoalloy is a low-cost and highly active catalyst towards the hydrolysis of sodium borohydride (NaBH₄). In this study, a facile and room-temperature hydrogen bubble-assisted method was developed to prepare porous Co–B nanoalloy (Co-B_bubble) materials exhibiting high catalytic activity. The obtained materials are characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, inductively coupled plasma-optical emission spectrometer, transmission electron microscopy and surface area experiments. It is found that the hydrogen bubbles generated in-situ in the reaction system can act as template, which played an important role in determining the porous architecture of the final Co–B product. In the hydrolysis of sodium borohydride for hydrogen generation, the porous Co-B_bubble nanoalloy materials exhibit high catalytic activity with mass normalized rate constant of 5.31 L_hydrogen min^?1 g_catalyst^?1; a value which is much higher than those obtained for many other Co–B catalysts recently reported in the literature. The apparent activation energy (Ea) of the catalytic process is found to be ca. 30 kJ mol^?1. It is proposed that the high catalytic performance and low cost of Co-B_bubble nanoalloy catalyst can be a promising material candidate in the hydrolysis of sodium borohydride for hydrogen production for commercial applications.     

Energy consumption and stability of the Ni-Mo electrodes for the alkaline hydrogen production at industrial conditions

Hydrogen production via electrolysis of water from alkaline aqueous electrolytes is a well-established conventional technology. However, the cost of hydrogen produced in such a way is high. To improve this process we have investigated in situ activation with Ni-Mo electrocatalytic material for electrodes. This two d-metal combination possesses one of the highest known activities for the HER. Ni-Mo based catalyst was not applied at industrial applications yet, because under industrial conditions (high temperature and concentrated alkaline solution), permanent destruction of the Ni-Mo alloy coating occurs. The most important result of this study is that the Ni-Mo deposit obtained by in situ activation, under industrial conditions, exhibit long term stability and the electrodes retain their high catalytic performance. The process of adding Ni-Mo activating compounds in situ exhibits savings of the energy consumption that can go beyond 20% in some cases.     

Novel nanostructured electrocatalysts for hydrogen evolution reaction in neutral and weak acidic solutions

Microbial electrolysis cells (MECs) provide an innovative bioelectrochemical approach for hydrogen production using microorganisms as biocatalysts. The development of cost-effective cathodes for near-neutral pH and ambient temperature conditions is the most critical challenge for the practical application of MEC technology. In this study, the electrocatalytic properties of electrodeposited onto carbon felt NiFe-, NiFeP- and NiFeCoP-nanostructures towards HER in neutral and weak acidic solutions were investigated. The voltage needed to initiate hydrogen production and the current production rates were estimated from obtained linear voltammograms. The developed composite materials possess much higher catalytic activity than bare carbon felt. The highest current production rate corresponding to 1.7 ± 0.1 m³H₂/day/m² was achieved with NiFeCoP/carbon felt electrodes. In addition, the applied modifications result in improvement of the corrosion resistance. The obtained results demonstrate that Ni-based nanomodified materials are promising electrocatalysts for HER in near-neutral electrolytes and could be applied as cathodes in MECs.     

Platinum–rare earth electrodes for hydrogen evolution in alkaline water electrolysis

In the new “Hydrogen Economy” concept, water electrolysis is considered one of the most promising technologies for hydrogen production. Novel electrocatalytic materials for the hydrogen electrode are being actively investigated to improve the energy efficiency of current electrolysers. Platinum (Pt) alloys are known to possess good catalytic activities towards the hydrogen evolution reaction (HER). However, virtually nothing is known about the effects of rare earth (RE) elements on the electrocatalytic behaviour of Pt towards the HER. In this study, the hydrogen discharge is evaluated in three different Pt–RE intermetallic alloy electrodes, namely Pt–Ce, Pt–Sm and Pt–Ho, all having equiatomic composition. The electrodes are tested in 8 M KOH aqueous electrolytes at temperatures ranging from 25 °C to 85 °C. Measurements of the HER by linear scan voltammetry allow the determination of several kinetic parameters, namely the Tafel coefficients, charge-transfer coefficients, and exchange current densities. Activation energies of 46, 59, 39, and 60 kJ mol⁻¹ are calculated for Pt, Pt–Ce, Pt–Sm and Pt–Ho electrodes, respectively. Results show that the addition of REs improves the activity of the Pt electrocatalyst. Studies are in progress to correlate the microstructure of the studied alloys with their performance towards the HER.     

Electrochemical characterization of a NiCo/Zn cathode for hydrogen generation

Hydrogen is considered to be the most promising candidate as a future energy carrier. One of the most used technologies for the electrolytic hydrogen production is alkaline water electrolysis. However, due to the high energy requirements, the cost of hydrogen produced in such a way is high.In continuous search to improve this process using advanced electrocatalytic materials for the hydrogen evolution reaction (HER), high area NiCo/Zn electrodes were prepared on AISI 304 stainless steel substrates by electrodeposition. After preparing, the alloys were leached of to remove part of the zinc and generate a porous layer (type Raney electrodes). The presence of a thin Ni layer between the substrate and the Raney coating favour the adherence of the latter. The porous NiCo/Zn electrode was characterized by SEM, EDX, confocal laser microscopy, and electrochemical impedance spectroscopy. HER on this electrode was evaluated in 30 wt.% KOH solution by means of polarization curves, hydrogen discharge curves, and galvanostatic tests. Results show that the developed electrode presents a most efficient behaviour for HER when comparing with the smooth Ni cathode. The high electrode activity was mainly attributed to the high surface area of the developed electrode.     

Electrocatalytic evolution of hydrogen on a novel SrPdO3 perovskite electrode

SrPdO₃ was prepared for the first time by the citrate method. XRD, SEM and TGA characterizations were carried out. The catalytic activity toward hydrogen evolution reaction (HER) was investigated, the activation energy, and reaction order and reaction mechanism have been determined using Tafel polarization and impedance techniques. The modified surface showed up to 100 times more efficiency towards electrocatalytic production of hydrogen. Adsorption of hydrogen on the catalyst was the rate-determining step and the reaction order at the surface of the catalyst is 0.86. The molar magnetic susceptibility was measured using Faraday's method and anti-ferromagnetic character was observed.     

Comparison of different electrode materials—Energy requirements in the electrolytic hydrogen evolution process

Hydrogen is one of the most widely produced commodities in the world economy. The basic technologies for producing hydrogen via the electrolysis of water have long been known. However, there are disadvantages when using this process. Two-thirds of the operation costs of the electrolyzers are electricity costs. The challenge, addressed by numerous companies and researchers in the last few years, is the cost cutting by increasing efficiency of the process.The aim of this work was the attempt to optimize the electrolytic hydrogen production from alkaline solution, through the variation of cathode materials and use of ionic activators.The part of our results shows the better electrocatalytic activity of intermetallic phases and the energy consumption is decreased when compared with the industrial data (4.5–5 kWh m⁻³ H₂). The role of ionic activator used is also very significant. These results give the opportunity for further research of cumulative effect of the intermetallic electrodes and ionic activators on industrial level.     

Ru–MoS2@PPy hollow nanowire as an ultra-stable catalyst for alkaline hydrogen evolution reaction

Electrocatalytic hydrogen evolution reaction (HER) is one of the green and effective method to produce clean hydrogen energy. However, the development of non-Pt HER catalysts with excellent catalytic activity and long-term stability still remains a great challenge. Herein, a vertically aligned core-shell structure material with hollow polypyrrole (PPy) nanowire as a core and Ru-doped MoS₂ (Ru–MoS₂) nanosheets as a shell is firstly reported as a highly efficient and ultra-stable catalyst for HER in alkaline solutions. Results indicate that Ru–MoS₂@PPy catalyst demands a low overpotential of 37 mV at 10 mA cm^?2. In addition, the overpotential at 100 mA cm^?2 is 157 mV and it is almost unchanged after 40,000 cyclic voltammetry cycles. The existence of PPy core not only ensures the vertical growth of MoS₂ nanosheets to expose more edge sites, but also promotes the rapid transfer of electrons, contributing to the improvement of catalytic activity. More importantly, the strong interface interaction between MoS₂ and PPy prevents the collapse of the vertical structure of MoS₂ sheets in the electrocatalytic process and greatly enhances the stability of catalysts, which offers an effective strategy to design and synthesize the HER catalysts with superior catalytic stability.     

Hydrogen generation from NaBH4 hydrolysis catalyzed by cobalt (0)-Deposited cross-linked polymer brushes: Optimization with an experimental design approach

Proposing a novel catalyst that achieves catalytic hydrolysis of metal hydrides is an important stage in developing a hydrogen storage system. In this study, a cross-linked gel brush-cobalt (0) composite (Co@P4VP_GB@PMC) has been synthesized to obtain hydrogen from NaBH₄ solution. The morphology, structure, and composition of the obtained catalyst have been characterized by, FTIR, SEM, EDX, BET, XRD, ICP-MS and XPS. The parameters that significantly affect the hydrolysis of NaBH₄ (such as NaBH₄ concentration, NaOH amount, catalyst amount, and temperature) have been investigated using response surface methodology (RSM), an optimization method that has gained increasing importance in recent years. The hydrogen generation rate (HGR) was 4499 mL/min g_cat for Co@P4VP_GB@PMC when the NaBH₄ amount was 241.52 mM, NaOH amount 5 wt%, catalyst amount 10.55 mg and temperature 58.9 °C. Moreover, the apparent activation energy (E_a) for the catalytic hydrolysis reaction has been 41.27 kJmol^-1 obtained under optimum conditions. Additionally, the Co@P4VP_GB@PMC catalyst displayed significant reusability performance for up to five cycles without major loss of its activity. Compared with metal catalysts, this new cross-linked polymer gel brush-cobalt catalyst has excellent potential applications for hydrogen production by hydrolysis of metal hydrides due to its simple synthesis, low cost, and the easy availability of raw materials.     

Cobalt-based composite films on electrochemically activated carbon cloth as high performance overall water splitting electrodes

An attractive approach to obtain effective and stable electrode for water electrolysis is to directly deposit the electrocatalyst on current collector surface. Herein, we show the influence of electrochemical activation of carbon cloth substrate on the morphology and electrocatalytic properties of bifunctional electrodes for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). A simple one-step electrodeposition technique was applied to directly grow mixed Co-based films on electrochemically activated carbon cloth (EACC) surface. The produced films are composed of metallic Co, and largely amorphous CoO/Co(OH)₂ phases. Variation of Co²⁺ concentration in the solution for electrodeposition enabled tuning the composition of mixed films in order to achieve the optimal HER and OER electrocatalytic performance in 0.1 M KOH. The synthesized electrodes require the overpotentials of 195 mV for HER and 340 mV for OER to deliver the current density of 10 mA/cm². The results indicate that the facile oxidation of carbon cloth prior to the electrodeposition decreases the overpotential at 10 mA/cm² by 150 and 60 mV for HER and OER respectively, thus opening the perspective of improving the activity of carbon-based self-supported composite electrocatalytic electrodes for advanced energy conversion processes.     

Hydrogen evolution and oxygen evolution reactions of pristine and alkali metal doped SnSe2 monolayer

Many transition metal di-selenides such as MoSe₂ and WSe₂ show good catalytic activity on their edges with limited active orientations. These metal di-selenides are actively being used as target material for increasing the number of electrocatalytic active sites and in turn to improve the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activities by increasing the ratio of edges to the basal plane. In present work, we have studied the activity of pristine and alkali atoms (Na, K and Ca) doped-SnSe₂ for HER and OER catalyst. The state-of-art density functional theory (DFT) based computations are performed for estimating the catalytic activity of the pristine and doped SnSe₂ by means of evaluating the adsorption and Gibbs free energies subjected to hydrogen and oxygen adsorption. Further, to get better prediction of adsorption energy on the individual catalytic surface, we have included the dispersion correction term to exchange-correlation functional. Results show that the pristine SnSe₂ is not a good HER catalyst when hydrogen is adsorbed on its basal plane. However, edge-sites show the good hydrogen adsorption and indicates that the edges of SnSe₂ are the most preferential site for hydrogen adsorption. As far as the catalytic activity of SnSe₂ with dopants is concerned, the Na-doped SnSe₂ among all shows the best catalytic activity over its edge-site; whereas K and Ca doped SnSe₂ show basal plane as preferred catalytic site. It is interesting to note that the disadvantage of low catalytic activity on basal plane of SnSe₂ can be improved by selective doping of alkali metals.     

Synthesis of Co2FeAl alloys as highly efficient electrocatalysts for alkaline hydrogen evolution reaction

The development of cost-effective non-precious metal electrocatalysts is a major challenge for water splitting applications, but it is important for the realization of renewable energy systems. Alloying has proved an effective way to design metal-based electrocatalysts, and by controlling the annealing temperature, the surface morphology and crystallinity of the alloy can be tuned to control the hydrogen evolution reaction (HER) performance. In this work, with a simple coprecipitation method, we have prepared Co₂FeAl alloys at different annealing temperatures (550 °C–670 °C), which exhibit excellent crystallinity and electrocatalytic performance for HER in alkaline solution. Among all conditions, the Co₂FeAl alloys prepared at 620 °C shows the better crystallinity and the higher purity, and it could achieve a low overpotential of 149 mV at 10 mA cm^?2 in alkaline solution. The overpotential demonstrates persistent stability with only 3 mV change after over 1000 cycles. Both density functional theory (DFT) calculations and experimental results revealed that alloying optimizes the electronic structure near the Fermi surface of the system, improving the electron transport efficiency and enhancing the catalytic activity. These Co₂FeAl alloys are appealing candidates for high-performance alkaline HER electrocatalytic electrodes in water electrolysis due to their outstanding electrocatalytic properties.     

Properties,mechanisms and advantages of metallic glass for electrocatalysis and HER in water splitting: A review

H₂ is one of the most promising and attractive alternative energy sources for fossil fuels to solve the current energy crisis and environmental problems. Hydrogen production from water electrocatalysis has become one of the most popular hydrogen production methods due to its high purity and environmental friendliness. The most commonly used catalyst for hydrogen evolution reaction (HER) is powdered Pt/C. However, the scarcity and complicated post-treatment processes severely limit its industrial application. Therefore, it is a key challenge to develop low-cost, high-performance self-supporting catalytic electrodes. Recently, metallic glasses (abbreviated as MGs) ribbons have attracted great interest in catalytic applications due to their unique short-range ordered and long-range disordered atomic structures. The metastable properties of MGs offer great potential for their application in HER. Here, this review introduces the preparation, application first. Secondly, we introduce the advantages and application progress of MGs as HER catalytic electrodes. Then, we summarize the factors affecting the catalytic performance of MGs in HER process. Finally, current challenges and future development prospects for realizing highly active and durable electrocatalysts are presented. This review aims to provide a guide for designing and developing MGs with high HER performance.     

Synthesis of non-noble NiMoO4–Ni(OH)2/NF bifunctional electrocatalyst and its application in water-urea electrolysis

Electrochemical water splitting to produce hydrogen is one of the most important technologies for energy storage and conversion. Urea oxidation reaction (UOR) with a lower electrode potential instead of oxygen evolution reaction (OER, water-splitting anode) in the water-urea electrolysis is an energy-saving approach. In this paper, NiMoO₄–Ni(OH)₂/NF is synthesized by hydrothermal reactions and explored as both hydrogen evolution reaction (HER) and UOR catalyst electrodes. This composite catalyst shows high catalytic bifunctional activities towards both HER and UOR. To validate both catalytic UOR and HER activities and durability, a two-electrode water-urea electrolyzer composed of NiMoO₄–Ni(OH)₂/NF as both anode and cathode materials is constructed (NiMoO₄–Ni(OH)₂/NF||NiMoO₄–Ni(OH)₂). Experiments show that a voltage of 1.341 V with a high stability (over 3000 CV cycles) can be achieved at 10 mA cm⁻², which are much better than those obtained using a Pt/C||IrO₂.     

Improved electrocatalytic methanol oxidation of NiO nanosheet arrays with synergistic high surface oxygen vacancy and Ni3+/Ni2+ ratio

The combination of anodic biomass electrooxidation and cathodic hydrogen evolution reaction is an effective strategy to realize energy saving hydrogen production and high value chemical products. Herein, we synthesized dense NiO nanosheet arrays on Ni foam using different heat-treatment temperature, including 400, 450 and 500 °C. The NiO prepared under 500 °C owns the highest oxygen defect concentration (58.1%) and Ni³⁺/Ni²⁺ ratio (3.13), giving the highest intrinsic activity for methanol electrocatalytic oxidation reaction. However, the NiO prepared at 400 °C (named as NiO-400) owns highest catalyst surface area and electrochemical surface area, giving the highest practical activity. Based on the above results, a facile method of surface modification by ultraviolet oxidation is proposed to improve the oxygen defect concentration (from 34.7% to 36.8%) and Ni³⁺/Ni²⁺ ratio (from 2.94 to 3.19) of NiO-400, and the catalytic current was increased by about 48.9%. This work provides some theoretical basis for improving the activity of biomass electrocatalytic oxidation of Ni-based materials.     

Nano P zeolite modified with Au/Cu bimetallic nanoparticles for enhanced hydrogen evolution reaction

In the present study, the excellent catalytic performance of Au/Cu bimetallic nanoparticles based on nano P zeolite modified carbon paste electrode (Au/Cu-NPZ-CPE) as one of the most promising electrocatalyst toward hydrogen production is introduced. Herein, nano P zeolite is synthesized by using agriculture residues, stem sweep ash with purity approximately 80.205 wt% of SiO₂ which provides attractive economically silica source for the preparation of inexpensive zeolite. For the preparation of Au/Cu-NPZ-CPE, ion exchange protocol followed by galvanic replacement reaction was employed to result Au/Cu embedded zeolite framework. By evaluating the electrocatalytic activity of proposed catalyst with linear sweep voltammetry and Tafel polarization, a low overpotential of 100 mV and high exchange current density (2.51 mA cm⁻²) are demonstrated which compares favorably to most previously reported electrocatalysts for hydrogen evolution reaction. Owing to the inherent porosity of synthesized nano P zeolite, it successfully prevents the aggregation of bimetallic nanoparticles which promotes the hydrogen evolution reaction. Particularly, low Tafel slope for offered catalyst (33 mV dec⁻¹) demonstrates the acceleration of hydrogen evolution reaction kinetics owing to the increase in the number of accessible active sites. Tafel slope of Au/Cu-NPZ-CPE is 3, 5, 6, 6.5 and 7 times lower than that for Au-NPZ-CPE, Cu-NPZ-CPE, Au/Cu-CPE, NPZ-CPE and CPE, respectively, which shows the best electrocatalytic activity among other modified carbon paste electrodes. Furthermore, the corresponding long term stability test by chronoamperometry method indicates that the current density reaches to nearly 91% of its primary value (after 5500 s) which provides the favorable practical demands of the catalyst in hydrogen production.