Earth-abundant Hydrogen Evolution Reaction Research Articles

Establishing stability of the novel layered ternary tri-chalogenide materials: Emergence of a new generation of earth abundant HER catalysts

Energetic and structural stability of thirteen novel ternary transition metal tri-chalcogenide layers, claimed to be promising catalysts for hydrogen evolution reaction (HER), are studied. Detailed analyses of electronic structure, and mechanical and phonon properties establish that ten out of the thirteen materials are stable. Further analyses establish that these are chemically in the same class as the known layered ternary transition metal tri-chalcogenide materials. These lead us to claim that it should be possible to synthesize these materials experimentally, thus enlarging the list of candidate materials that can replace platinum as HER catalysts.

Defect-rich MnxOy complex Fe–Ni sulfide heterogeneous electrocatalyst for a highly efficient hydrogen evolution reaction

Designing earth-abundant hydrogen evolution reaction (HER) electrocatalysts with superior performance and eminent stability is the key to the practical production of high purity hydrogen. In the present work, Mn oxides with various valence state complex Fe–Ni sulfide (MnxOy@FNS) heterogeneous materials were successfully fabricated through a feasible two-step hydrothermal process and can be directly used as active and efficient HER electrodes in alkaline media. This binder-free and defect-rich catalyst barely requires 105 and 365 mV to achieve −10 and −500 mA cm−2, respectively. Profiting from the disordered structure and the efficient interfacial effects between Mn oxides and Fe–Ni sulfide (FNS), this heterogeneous catalyst reveals sufficient electroactive sites, ample active edges and optimal electroconductivity. Additionally, during the 20 h HER reaction, the MnxOy@FNS electrode exhibits outstanding durability.

A durable and pH-universal self-standing MoC\u2013Mo2C heterojunction electrode for efficient hydrogen evolution reaction

Efficient water electrolyzers are constrained by the lack of low-cost and earth-abundant hydrogen evolution reaction (HER) catalysts that can operate at industry-level conditions and be prepared with a facile process. Here we report a self-standing MoC–Mo2C catalytic electrode prepared via a one-step electro-carbiding approach using CO2 as the feedstock. The outstanding HER performances of the MoC–Mo2C electrode with low overpotentials at 500 mA cm−2 in both acidic (256 mV) and alkaline electrolytes (292 mV), long-lasting lifetime of over 2400 h (100 d), and high-temperature performance (70 oC) are due to the self-standing hydrophilic porous surface, intrinsic mechanical strength and self-grown MoC (001)–Mo2C (101) heterojunctions that have a ΔGH* value of −0.13 eV in acidic condition, and the energy barrier of 1.15 eV for water dissociation in alkaline solution. The preparation of a large electrode (3 cm × 11.5 cm) demonstrates the possibility of scaling up this process to prepare various carbide electrodes with rationally designed structures, tunable compositions, and favorable properties.

Edge-Rich Reduced Graphene Oxide Embedded in Silica-Based Laminated Ceramic Composites for Efficient and Robust Electrocatalytic Hydrogen Evolution.

To mitigate the energy crisis and environmental pollution, efficient and earth-abundant hydrogen evolution reaction (HER) electrocatalysts are essential for hydrogen production through electrochemical water splitting. Graphene-based materials as metal-free catalysts have attracted significant attention but suffer from insufficient activity and stability. Therefore, a novel and economical approach is developed to prepare highly active, robust, and self-supported reduced graphene oxide (rGO)/SiO2 ceramic composites as electrocatalysts in HER. Through intercalation and pressure sintering, the rGO sheets are parallelly aligned and embedded into a dense and chemically inert SiO2 matrix, ensuring the electrical conductivity and stability of the prepared composites. After directional cutting, the edges of the oriented rGO sheets become fully exposed on the composite surface, acting as highly electrocatalytic active sites in HER, as confirmed by density functional theory calculations. The 4 vol% rGO/SiO2 composite displays superior electrocatalytic performance, featuring a low overpotential (134mV) at a current density of 10mA cm-2 , a small Tafel slope (103mV dec-1 ), and excellent catalytic durability in 0.5 m H2 SO4 . This study provides a new yet cost-effective strategy to prepare metal-free, robust, and edge-rich rGO/ceramic composites as a highly electrocatalytic active catalyst for HER applications.

Dual-phase amorphous-nanocrystalline nanoporous sites activated in Mo inserted CuTi metallic glass as efficient electrocatalysts for hydrogen evolution reaction

The production of noble metal-free, high-performance, earth-abundant hydrogen evolution reaction (HER) electrocatalysts is a challenging search but indispensably a vital issue for green energy conversion and production. Herein, we report a nanoporous self-supported CuTiMo site nanostructured from Cu60Ti37Mo3 metallic glass as a highly efficient electrocatalyst for HER. The development of nanoporous structure from metallic glassy alloy rather than the conventional crystalline alloy is carried out, and a comprehensive plausible working mechanism of nanoporous structure development is outlined. The novelty of the present research is the nanostructuring of metallic glasses to form crystalline and amorphous dual sites. The dual phased nanoporous electrocatalyst exhibits high catalytic activity comparable to standard Pt-catalyst at higher current densities (>60 mA cm−2). The electrocatalyst is stable even at high current densities (>100 mA cm−2) and needs much lesser overpotential than that of standard Pt/C catalyst for HER reaction at high current densities. The dealloying of defect-free metallic glasses leads to the formation of a large number of catalytic active sites, and the introduction of Mo into the CuTi matrix leads to accelerated H2 adsorption/desorption kinetics. The dealloyed metallic glass requires an overpotential of 220 mV vs. RHE to attain a current density of 100 mA cm−2 in an alkaline HER reaction. Based on the advantages of nanoporous structure development from highly metastable metallic glasses, the high active surface area of nanoporous structure on a high conductive substrate, the exceptional stability for long term and at high current densities, the proposed nanoporous metallic glass composite electrode is of significance for a diversity of applications for green energy production.

Transition Metal Sulfide-Based Electrocatalysts for Hydrogen Evolution Reaction in Alkaline Environment

Hydrogen already plays a key role in many industrial processes and the interest in this compound has recently increased since it is pointed-out as a promising future energy carrier. Besides to present a high energy yield, no greenhouse gas is produced during its oxidation. However, most of current hydrogen production still comes from fossil feedstock and, due to environmental concerns, methods aiming the renewable, cleaner and economically suitable production of hydrogen are being developed.Hydrogen production from water, in a process called “water electrolysis”, has been receiving great attention because if it is coupled to a renewable source of energy, it results in zero carbon emission. In this process, water is splitted to originate two gases, hydrogen at the cathode and oxygen at the anode, both containing high purity. The reactions responsible for their production in each half-cell are called hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively.The use of catalysts is compulsory in order to minimize the overpotential of aforementioned reactions and, consequently, increase process efficiency. Noble metal-based materials, mainly Pt, Ru and Ir, remain as benchmark to catalyze these reactions, but their high-cost and scarcity are responsible for limiting their application in large scale. In order to overcome these barriers, new candidate catalysts must be searched and they need to be active, stable, cheap and sustainable.Nørskov et al. [1] presented one important, but not unique, indicator for highly active HER catalysts, the free energy of H adsorption (∆GH 0) on the sites; the closer to zero, the better. They also brought attention to the similar sulfur coordination to metals in both MoS2 edges and active sites of nitrogenase, an efficient hydrogen evolution enzyme. Thus, authors stated that edge sites of MoS2 materials are active since they attend thermoneutrality criterion, although their basal planes are inert. Later, it was experimentally confirmed by Jaramillo et al. [2]. As consequence, further works have also shown good activity of other transition metal sulfides (TMS) towards HER and, therefore, it has become a promising class of materials to replace the expensive Pt-based electrocatalysts.Noteworthy, Nørskov et al. [1] performed calculations that take into account an acidic environment and, for this reason, only ∆GH 0 descriptor was used to estimate HER activity. However, HER in alkaline medium brings an additional step of water dissociation, responsible to generate the proton which is further reduced to adsorbed hydrogen specie; such step may increase energy consumption of reaction. Furthermore, lower binding energy of water compared to hydronium and the interaction of hydroxyl groups with the catalytic sites, abundant in high pH’s, may play a key role in catalysts’ activity. As result, the mechanism of HER in alkaline electrolyte is more complex. Despite that, the alkaline environment allows the application of wider range of materials, including non-noble metal-based ones, in HER and OER. This, summed up to new developments in alkaline exchange membranes, make it worth to search for materials which may be applied in alkaline exchange membrane water electrolyzers (AEMWE).In the present work, by applying the synthesis reported by Li et al. [3] with modifications, several TMS were produced by hydrothermal method employing sodium diethyldithiocarbamate (C5H10NS2Na), non-conventional precursor, as sulfur source. Adjusts in synthesis parameters were performed aiming the development of earth-abundant HER electrocatalysts to be applied in AEMWE devices. As preliminary results, 225 and 50 mV overpotentials were measured at -10 and -100 mA cm-2, respectively on HER polarization curves obtained in 1 M KOH electrolyte on MoSx-based cathodes, compared to a commercial 40% Pt/C material as reference. Doping strategies with M-M’ TMS synthesis are being implemented for improving HER efficiency. Acknowledgements: This work was mainly conducted within the framework of a PhD thesis financially supported by the European Union (ERDF), GrandAngoulême and Région Nouvelle-Aquitaine. References Hinnemann, P.G. Moses, J. Bonde, K.P. Jørgensen, J.H. Nielsen, S. Horch, I. Chorkendorff, J.K. Nørskov, J. Am. Chem. Soc. 122 (2005) 5308-5309.F. Jaramillo, K.P. Jørgensen, J. Bonde, J.H. Nielsen, S. Horch, I. Chorkendorff, Science 317 (2007) 100-102. Li, M. Xiao, Y. Zhou, D. Zhang, H. Wang, X. Liu, D. Wang, W. Wang, Dalton Trans. 47 (2018) 14917-14923.

Role of Redox Active Ligand of a Cobalt-Mabiq Complex in the Hydrogen Evolution Reaction

In nature, hydrogen is generated by a family of enzymes known as the hydrogenases, which use Fe and/or Ni as cofactors. Inspired by metalloenzyme cofactors, many earth-abundant hydrogen evolution reaction (HER) catalysts have been developed over the last decade, but their HER activity, chemical stability under operation, and overpotential could still be significantly improved. The H2 evolution mechanisms of many molecular catalysts are based on metal hydride formation, however, the role of redox-active ligands has attracted attention recently. Such systems may operate via alternative H2 evolution pathways involving mainly ligand-assisted and ligand-based routes,1, 2 in which the ligands act as H-atom or hydride reservoirs. Electron or proton storage by redox-active ligands could therewith lead to improved HER kinetics and decreased overpotentials.We will present our studies on the H2 evolution activity and possible HER pathways of a cobalt complex, containing a redox active macrocyclic biquinazoline ligand (Mabiq).3, 4 In the literature an electron transfer series of Co-Mabiq complexes exemplifies ligand-centered reduction among the formally ‘low valent’ compounds.5 The role of the ligand in H2 the evolution activity of a Co-Mabiq complex is the main focus of our study. The electrocatalytic behavior of [CoII(Mabiq)(THF)](PF6) (CoMbq) was studied in organic media (acetonitrile) using para-cyanoanilinium as the proton source.4 Besides the confirmed H2 evolution by CoMbq, the combined on-line electrochemical mass spectrometry (OEMS) and rotating ring disk electrode (RRDE) techniques denote a pre-catalytic process that involves formation of a protonated, two electron reduced intermediate (Figure1). Our results further indicate a competing deactivation pathway that is either time dependent or turnover dependent.The potential intermediate Co-Mabiq complexes in various oxidation states5 each exhibit distinct absorption spectroscopic features. Hence, in our study, bulk electrolysis and UV-Vis absorption spectrometry were further carried out to characterize the active and inactive CoMbq intermediates. Based on these findings, modifications to the ligand backbone may prevent the formation of the inactive intermediates that lead to inhibition of the deactivation pathway, and may therewith enable a prolonged activity for H2 evolution by the CoMbq complex. The combined results of our studies provide an insight into the role of Mabiq and redox-active ligands in general in the HER pathway while also providing a comprehensive toolbox of electrochemical and spectroscopic techniques to allow a deep understanding for this class of molecular H2 evolution catalysts.

2H-MoS2 on Mo2CTx MXene Nanohybrid for Efficient and Durable Electrocatalytic Hydrogen Evolution.

The development of highly efficient and durable earth-abundant hydrogen evolution reaction (HER) catalysts is crucial for the extensive implementation of the hydrogen economy. Members of the 2D MXenes family, particularly Mo2CTx, have recently been identified as promising HER catalysts. However, their inherent oxidative instability in air and aqueous electrolyte solutions is hindering their widespread use. Herein, we present a simple and scalable method to circumvent adventitious oxidation in Mo2CTx MXenes via in situ sulfidation to form a Mo2CTx/2H-MoS2 nanohybrid. The intimate epitaxial coupling at the Mo2CTx/2H-MoS2 nanohybrid interface afforded superior HER activities, requiring only 119 or 182 mV overpotential to yield -10 or -100 mA cm-2geom current densities, respectively. Density functional theory calculations reveal strongest interfacial adhesion was found within the nanohybrid structure as compared to the physisorbed nanohybrid, and the possibility to tune the HER overpotential through manipulating the extent of MXene sulfidation. Critically, the presence of 2H-MoS2 suppresses further oxidation of the MXene layer, enabling the nanohybrid to sustain industrially relevant current densities of over -450 mA cm-2geom with exceptional durability. Less than 30 mV overpotential degradation was observed after 10 continuous days of electrolysis at a fixed -10 mA cm-2geom current density or 100,000 successive cyclic voltammetry cycles. The exceptional HER durability of the Mo2CTx/2H-MoS2 nanohybrid presents a major step forward to realize practical implementation of MXenes as noble metal free catalysts for broad-based applications in water splitting and energy conversion.

Ultrastable molybdenum disulfide-based electrocatalyst for hydrogen evolution in acidic media

Despite the incredible success in reducing the overpotential of nonprecious catalysts for acidic hydrogen evolution reaction (HER) in the past few years, the stability of most platinum-free electrocatalysts is still poor. Here, we report an ultrastable electrocatalyst for acidic HER based on two-dimensional (2D) molybdenum disulfide (MoS2) doped with trace amount of palladium (<5 μg cm−2), which creates sulfur vacancies (S-vacancies). The optimized catalyst shows stable operation over 1000 h at 10 mA cm−2 with overpotential of 106 mV. The MoS2 catalyst is stabilized on a defective vertical graphene support, where the strong interaction at the 2D-2D interface increases the adhesion between the catalyst and the support. Palladium (Pd) doping generates rich sulfur vacancies in MoS2 that have a twofold role: (1) increasing hydrogen adsorption energy, which enhances activity; and (2) further increasing the adhesion between graphene support and defective MoS2, and thus enhancing stability. Complementary theoretical studies reveal the reaction pathways for substitutional doping, where the Mo-vacancy sites are prior to be doped by Pd. Our work thus offers a strategy for making stable, efficient, and earth-abundant HER catalysts with strong potential to replace platinum for PEM electrolysis.

Stabilizing sulfur vacancy defects by performing "click" chemistry of ultrafine palladium to trigger a high-efficiency hydrogen evolution of MoS2.

Defect engineering is widely applied in transition metal dichalcogenides to produce high-purity hydrogen. However, the instability of vacancy states on catalysis still remains a considerable challenge. Here, our first-principles calculations showed that, by optimizing the asymmetric S vacancy in the highly asymmetric 1T' crystal of layered bitransition metal dichalcogenides (Co-MoS2) in light of Pd modulation, the relative amount of metastable phase and the quantity of active sites in the structure can be reduced and increased, respectively, leading to a further boosted hydrogen evolution reaction (HER) activity toward layered bi-transition metal dichalcogenides. Thus, we then used a "click" chemistry strategy to make such a catalyst with engineered unsaturated sulfur edges via a strong coupling effect between ultrafine Pd ensembles and Co-MoS2 nanosheets. As expected, the Pd-modulated Co-MoS2 nanosheets exhibited a very low overpotential of 60 mV at 10 mA cm-2 with a small Tafel slope (56 mV dec-1) for the HER in 1.0 M PBS, comparable to those of commercial Pt/C. In addition, their high HER activity was retained in acidic and alkaline conditions. Both the theoretical and experimental results revealed that Pd ensembles can efficiently activate and stabilize the inert basal plane S sites during HER processes as a result of the formation of Pd-S in Co-MoS2. This work not only provides a deeper understanding of the correlation between defect sites and intrinsic HER catalytic properties for transition metal chalcogenide (TMD)-based catalysts, but also offers new insights into better designing earth-abundant HER catalysts displaying high efficiency and durability.

Boosting Hydrogen Transfer during Volmer Reaction at Oxides/Metal Nanocomposites for Efficient Alkaline Hydrogen Evolution

Developing efficient and robust Earth-abundant hydrogen evolution reaction (HER) catalysts is crucial for the scalable and sustainable production of hydrogen. This study builds on the promising concept of oxide/metal nanocomposites, namely NiO/Ni, by incorporating another metal (in this case, Mo) into NiO to tune the adsorption energy of hydrogen (H). Theoretical and experimental approaches are combined to design Mo-NiO/Ni nanocomposites for efficient HER in alkaline media. The incorporation of Mo into NiO weakens the adsorption of H, favoring its transfer to nearby Ni active sites to accelerate the Volmer reaction, and also stabilizes the crystal structure of NiO. The Mo-NiO/Ni catalyst exhibits a 50 mV overpotential at a current density of −10 mA cm–2 with a Tafel slope of 86 mV dec–1, indicating that it is one of the most promising alkaline HER electrocatalysts reported to date. These findings suggest design principles for inexpensive, efficient, and high-performance Earth-abundant HER catalysts.

Rational design of phosphorus-doped cobalt sulfides electrocatalysts for hydrogen evolution

Moderate anionic doping is an effective approach to improve the performance of electrocatalysts toward hydrogen evolution reaction (HER) since it can adjust the electronic structure, active site, and phase. The reported studies mainly focus on designing P doped CoS2, while other phases of cobalt sulfide, such as Co1−xS and Co9S8 doped with P are rarely investigated for HER electrocatalysts. Herein, various cobalt sulfides (including CoS2/Co1−xS, Co1−xS, and Co9S8) doped with P are anchored on carbon cloth through a facile hydrothermal method. Among tested electrocatalysts, P doped Co1−xS exhibits excellent electrocatalytic performance with an overpotential of 110 and 165 mV (vs. RHE) for current densities of 10 and 100 mA·cm−2, respectively. Density functional theory calculations reveal that P doped Co1−xS possesses a smaller bandgap and more optimal hydrogen adsorption sites than pristine Co1−xS. This work initially investigates various cobalt sulfides doped with P and further gets insight into the activity improvement mechanism of P doping, which could guide the design of earth-abundant HER electrocatalysts for the “hydrogen economy”.

CoP3/CoMoP Heterogeneous Nanosheet Arrays as Robust Electrocatalyst for pH-Universal Hydrogen Evolution Reaction

Design and fabrication of a highly active and earth-abundant hydrogen evolution reaction (HER) electrocatalyst which can work in a wide range of pHs are pivotal for sustainable hydrogen production....

Enhancing Durability and Photoelectrochemical Performance of the Earth Abundant Ni-Mo/TiO2 /CdS/CIGS Photocathode under Various pH Conditions.

Cu(In,Ga)(S,Se)2 (CIGS) is a promising photocathode material owing to its high absorption coefficient, adjustable band gap, and suitable band edge for the hydrogen evolution reaction (HER). However, most CIGS photocathodes have suffered from instability in applications that require a wide range of pH conditions and have utilized noble metal HER catalysts to achieve a high performance. Thus, improving the durability of the CIGS photocathode under various pH conditions and developing a cost-effective non-noble metal catalyst are critical issues in the photoelectrochemical (PEC) application of this promising photocathode material. Here, we catalyze the CIGS photocathode with Ni-Mo as a non-noble metal to enhance the PEC efficiency, and we employ atomically grown TiO2 to passivate the CdS/CIGS surface and improve the stability under a wide range of pH conditions. Our Ni-Mo alloy exhibits the best HER catalytic activity among reported earth-abundant HER catalysts in both acidic and alkaline solutions. The Ni-Mo/CdS/CIGS photocathode yields an onset potential of 0.5 V (vs. RHE) and a short-circuit photocurrent density as high as 15-25 mA cm-2 under various pH conditions ranging from 0.4 to 14, which is highly comparable to that of Pt/CdS/CIGS. Furthermore, the passivation of CdS/CIGS with a thin TiO2 layer, obtained by atomic layer deposition, effectively prevents the photocorrosion of CdS and the dissolution of the Mo back contact, which are the main causes of the degradation of the photocathode. The optimized Ni-Mo/TiO2 /CdS/CIGS photocathode produces a stable photocurrent density at 0 VRHE for 100 minutes except under strong alkaline conditions. The current work presents a very useful method to improve the efficiency and durability of the CIGS photocathodes with an earth-abundant metal catalyst, which completely replaces Pt.

Single-atom supported on graphene grain boundary as an efficient electrocatalyst for hydrogen evolution reaction

Embedding a single atom into the supported catalysts is the most effective way to maximize the catalytic efficiency, holding promise for developing low-cost electrocatalysts. Grain boundaries in graphene display unique structures and have attracted great research efforts in electronic properties, catalysis and sensors. By using density function theory (DFT) calculations, we systematically investigated the potential of a single transition metal (TM) atom (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ag, Au, Pt) supported on the experimentally realised 558 grain boundary (GB), as a highly efficient electrocatalyst for hydrogen evolution reaction (HER). We find that the Fe, Co, Ni and V atom anchored on 558 GB can substantially tune the free energy of hydrogen adsorption to a more optimal value, especially for the V atom (ΔGH∗ = −0.01 eV), which is very close to, or even better than the most active Pt and MoS2 catalysts. This feature is attributed to the charge transfer between TM atom and the adsorbed H atom, which significantly promotes the proton adsorption and the reduction of kinetics. In addition, a large number of electronic states near the Fermi level ensure efficient electron transfer. Our study may provide a new cost-effective, highly active and earth-abundant HER electrocatalyst for hydrogen production.

Electrosynthesis of Bifunctional WS3-x /Reduced Graphene Oxide Hybrid for Hydrogen Evolution Reaction and Oxygen Reduction Reaction Electrocatalysis.

A multitude of research into the application of transition-metal dichalcogenides as earth-abundant hydrogen evolution reaction (HER) electrocatalysts has been conducted. However, current synthetic methods generally deploy environmentally harmful chemicals and energy-consuming reaction conditions, despite the primary intent to attain renewable energy production. Here, the desirable properties of tungsten sulfide and reduced graphene oxide (rGO) have been combined and hybrid materials have been fabricated through simultaneous electrochemical reduction and synthesis, as a versatile and environmentally benign alternative to conventional fabrication techniques. Through concurrent studies of three rGO materials, the precursor of which was graphene oxide (GO), produced by Hummers, Staudenmaier, or Hofmann oxidation methods, the importance of the choice of oxidation method employed prior to the fabrication of the hybrid was shown. In this cardinal study, a mixed WS2 /WS3 film-like material (WS3-x ) was synthesized directly onto GO-modified glassy carbon electrodes by cyclic voltammetry and the resultant hybrid materials (WS3-x /rGO) were thoroughly characterized by SEM, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. The excellent bifunctional electrocatalytic performances of WS3-x /rGO towards both HER and oxygen reduction reaction stemmed from the coupled impacts of amplified electrical conductivity and surface area of rGO; the presence of metallic species within rGO, resulting from the oxidation process; and the amount of WS3-x successfully electrodeposited in the hybrid. The efficacious fabrication of the WS3-x /rGO composite through electrosynthesis reveals an innovative and eco-friendly methodology for the development of cost-effective and highly active bifunctional electrocatalysts for renewable energy generation.

Highly efficient and durable MoNiNC catalyst for hydrogen evolution reaction

We report a carbothermal ammonia reduction (CAR) strategy for one-pot preparation of highly efficient and durable hydrogen evolution reaction (HER) electrocatalyst composed of earth abundant early transition metals. In this strategy, resin is applied both as the pre-binder and carbon source, and Pluronic F127 as the structure-directing agent. Upon annealing in NH3, the Mo-containing precursor on Ni foam undergoes the CAR, and simultaneously Ni from the substrate diffuses out, resulting in the formation of a quaternary complex structure of molybdenum-nickel bimetallic carbonitride (MoNiNC). The as-prepared electrode showed outstanding HER performance with an overpotential of 150mV at 50mAcm−2 and maintained steady hydrogen bubble evolution for continuous 48h. Our strategy offers a quick and simple way to fabricate earth-abundant HER electrode with highly efficient and durable electrocatalytic performance.

Sponge-like nickel phosphide–carbon nanotube hybrid electrodes for efficient hydrogen evolution over a wide pH range

Cost-effective hydrogen production via electrolysis of water requires efficient and durable earth-abundant catalysts for the hydrogen evolution reaction (HER) over a wide pH range. Herein, we report sponge-like nickel phosphide–carbon nanotube (Ni x P/CNT) hybrid electrodes that were prepared by facile cyclic voltammetric deposition of amorphous Ni x P catalysts onto the threedimensional (3D) porous CNT support. These compounds exhibit superior catalytic activity for sustained hydrogen evolution in acidic, neutral, and basic media. In particular, the Ni x P/CNT electrodes generate cathodic currents of 10 and 100 mA·cm−2 at overpotentials of 105 and 226 mV, respectively, in a 1 M phosphate buffer solution (pH = 6.5) with a Tafel slope of 100 mV·dec−1; the currents were stable for over 110 h without obvious decay. Our results suggest that the 3D porous CNT electrode supports could serve as a general platform for earth-abundant HER catalysts for the development of highly efficient electrodes for hydrogen production.

Recent progress on earth abundant hydrogen evolution reaction and oxygen evolution reaction bifunctional electrocatalyst for overall water splitting in alkaline media

Abstract Electrochemical water-splitting is one of the promising ways for producing clean chemical fuel (Hydrogen) while cheap-earth-abundant-bifunctional-electrocatalyst is one of the possible way for improving the overall cost efficiency of water-splitting. This paper reviews the chemical state, hydrogen and oxygen evolution reaction activity in alkaline media, overall water-splitting performance in alkaline media, stability, and possible-factors for improving its efficiency of various kinds of recently reported electrocatalyst such as Ni-P, Co-P, Ni-Co-P, graphene-Co-P, O/N/C-Co/Ni, Ni-S, B-Ni/Co, Ni-Co, Mo, Se, Fe, Mn/Zn/Ti, and metal-free based earth-abundant-bifunctional-electrocatalyst. This paper also reviews and highlights the remarkable water splitting performance of the earth-abundant-bifunctional-electrocatalyst those exhibit better or well comparable with Pt/C//RuO2.

Electrochemical fabrication of porous Ni-Cu alloy nanosheets with high catalytic activity for hydrogen evolution

Porous Ni-Cu alloy films composed of nanosheets are directly fabricated on Cu substrate using a facile potentiostatic electrodeposition approach from a 1:2 choline chloride-ethylene glycol eutectic solvent (ethaline) containing nickel chloride and copper chloride. Electrochemical co-deposition of Ni-Cu alloy in ethaline is found to be thermodynamically favorable in comparison to conventional aqueous solutions. The deposition process occurs via an instantaneous nucleation and growth of nanoparticles at the initial stage and develops vertically to form nanoporous structures arrayed with nanosheets over deposition time. The as-prepared porous Ni-Cu alloy nanosheet arrays exhibit enhanced electrocatalytic activity for the hydrogen evolution reaction (HER) in alkaline media, which displays a small Tafel slope of 57.2mVdec−1 with a low onset potential of −48mV vs. RHE at an optimal condition. It requires small overpotentials of −128 and −150mV to drive catalytic current densities of 10 and 20mAcm−2, respectively. This facile electrodeposition method performed in ethaline provides an efficient way to fabricate porous Ni-based alloy nanosheets directly on a current collector, which is a promising technology for the synthesis of earth-abundant HER electrocatalysts.