Electrocatalytic activity and electrochemical hydrogen storage of Ni-La alloy prepared by electrodeposition from aqueous electrolyte

Ni睱a alloy coating was prepared by electrodeposition. The effect of cathodic current density on the La content of the alloy coatings was discussed. It is found that the content of La in the alloy increases with increasing the cathodic current density. The microstructures and codeposition mechanism of Ni La alloy coatings were investigated by means of X ray diffraction (XRD) and cyclic voltammetry (CV). The results demonstrate that the Ni La alloy is FCC and codeposited by the induced mechanism. The hydrogen evolution reaction (HER) on the electrodeposited Ni La alloy electrodes in alkaline solution was evaluated by Tafel polarization curves. It is found that La Ni alloy coating exhibites much higher exchange current density for HER than pure Ni electrode, and that the exchange current density increases with increasing the La content of alloys. The good electrocatalytic activity for HER of this Ni La alloy is attributed to the synergism of the electronic structure of La and Ni. The electrodeposited La Ni alloys have a certain electrochemical hydrogen storage capacity of 34 ～ 143?mAh/g, which increases with increasing the La content of alloys.

In-situ hydrothermal synthesis of Ni−MoO_(2)heterostructure on porous bulk NiMo alloy for efficient hydrogen evolution reaction

The Ni−MoO_(2) heterostructure was synthesized in suit on porous bulk NiMo alloy by a facile powder metallurgy and hydrothermal method.The results of field emission scanning electron microscopy(SEM),field emission transmission electron microscopy(TEM)and X-ray photoelectron spectroscopy(XPS)reveal that the as-prepared electrode possesses the heterostructure and a layer of Ni(OH)_(2) nanosheets is formed on the surface of Ni−MoO_(2) electrode simultaneously after hydrothermal treatment,which provides abundant interface and much active sites,as well as much active specific surface area.The results of hydrogen evolution reaction indicate that the Ni−MoO_(2) heterostructure electrode exhibits excellent catalytic performance,requiring only 41 mV overpotential to reach the current density of 10 mA/cm^(2).It also possesses a small Tafel slope of 52.7 mV/dec and long-term stability of electrolysis in alkaline medium.

Pollen-like self-supported FeIr alloy for improved hydrogen evolution reaction in acid electrolyte

Ir is recognized as efficient catalyst for hydrogen evolution reaction(HER).The high price,however,has hindered its application in the production of hydrogen.In this work,we prepared the self-supported FeIr alloy nanoparticles,taking advantage of solid-state synthesis method.The as-prepared FeIr alloy possesses a novel morphology of pollen,which is consist of smaller FeIr nanoparticles.DFT calculations reveal that the change of the free Gibbs for Ir is negative after the adsorption of active H,while it is positive for the case of Fe.Thus,the alloying of Fe and Ir not only effectively reduces the cost,but also can achieve more adequate adsorption of active H species.Benefitting from this,the as-prepared FeIr alloy nanoparticle exhibits superior HER performance with an overpotential of 19 m V at a current density of 10 m V/cm^(2)and a Tafel slope of 32 m V/dec,when tested in 0.5 M H_(2)SO_(4),better than pure Ir and Pt/C.This work paves the way to the exploration of efficient alloy electrocatalysts for HER.

Electrodeposition of self-supported NiMo amorphous coating as an efficient and stable catalyst for hydrogen evolution reaction

NiMo-based materials have been identified as potential candidates of Pt/C electrocatalysts for hydrogen evolution reaction(HER)due to appropriate binding energy to hydrogen,and good resistance to corrosive environments.However,little work has been carried out to enhance the catalytic performance in large-scale water-alkali electrolysis.The NoMo amorphous coating,as a highefficient and cost-effective catalyst toward HER,was synthesized by a facile electrodeposition strategy in this study.The effects of the pH value of electrolyte on the structure and HER activity of NiMo coating were investigated.The as-prepared NiMo_((pH10))exhibited the highest HER activity with overpotentials of 63.9 and 157.1 mV(vs.RHE,with 80%potential drop due to electrical resistance(iR)compensation)at the current density of-10 mA·cm^(-2)and-100 mA·cm^(-2).This NiMo_((pH10))coating also had excellent long-term durability of up to100 h stable operation under the constant current density of-100 mA·cm^(-2).The rapid HER kinetics and outstanding endurance can be ascribed to the NiMo compact coating with amorphous structures as well as good contact between NiMo coating and Ni foam substrate,endowing it grand feasibility in practical industrial applications.

Three-Dimensional Hierarchical Nanostructured Cu/Ni–Co Coating Electrode for Hydrogen Evolution Reaction in Alkaline Media

In this work,three-dimensional hierarchical nickel–cobalt alloy coating for hydrogen evolution cathode was fabricated by electrodeposition processes.The coatings’morphology evolves from sea cucumber-like nanostructure to caterpillar-like one with the increase of cobalt content.A large amount of nanometric‘‘steps,’’served as the active sites for hydrogen evolution reaction,were observed.According to Tafel polarization measurements,the exchange current density of the as-synthesized coating with hierarchical nanostructure was 21.9 times compared with that of flat nickel coating.In addition,the hierarchical coating also displayed good electrochemical stability from the galvanostatic test.

Millisecond-timescale electrodeposition of platinum atom-doped molybdenum oxide as an efficient electrocatalyst for hydrogen evolution reaction

We present a straightforward method for one-pot electrodeposition of platinum atoms-doped molybdenum oxide(Pt·MoO_(3-x))films and show their superior electrocatalytic activity in the hydrogen evolution reaction(HER).A~15-nm-thick Pt·MoO_(3-x) film was prepared by one-pot electrodeposition at-0.8 V for 1 ms.Due to considerably different solute concentrations,the content of Pt atoms in the electrode-posited composite electrocatalyst is low.No Pt crystals or islands were observed on the flat Pt-MoO_(3-x) films,indicating that Pt atoms were homogeneously dispersed within the MoO_(3-x) thin film.The catalytic performance and physicochemical features of Pt·MoO_(3-x) as a HER electrocatalyst were characterized.The results showed that our Pt·MoO_(3-x) film exhibits 23-and 11-times higher current density than Pt and MoO_(3-x) electrodeposited individually under the same conditions,respectively.It was found that the dramatic enhancement in the HER performance was principally due to the abundant oxygen defects.The use of the developed one-pot electrodeposition and doping method can potentially be extended to various catalytically active metal oxides or hydroxides for enhanced performance in various energy storage and conversion applications.

Bifunctional interstitial phosphorous doping strategy boosts platinum-zinc alloy for efficient ammonia oxidation reaction and hydrogen evolution reaction

It is still a lack of bifunctional catalysts for ammonia oxidation reaction(AOR)and hydrogen evolution reaction(HER)due to their different reaction mechanisms.In this work,P is doped into PtZn alloy by calcination with NaH_(2)PO_(2) as P source to induce the lattice tensile strain of Pt and the electronic interaction between P and Zn,which optimizes the AOR and HER activity simultaneously.The sample with the optimal P content can drive the AOR peak current density of 293.6 mA·mgPt^(-1),which is almost 2.7 times of Pt.For HER,the overpotential at^(-1)0 mA·cm^(-2) is only 23 mV with Tafel slope of 34.1 mV·dec^(-1).Furthermore,only 0.59 V is needed to obtain 50 mA·mgPt^(-1) for ammonia electrolysis under a two-electrode system.Therefore,this work shows an ingenious method to design bifunctional catalysts for ammonia electrolysis.

Pt nanodendrites with a PtIr alloy surface structure exhibit excellent stability toward acidic hydrogen evolution reaction

The development of effective and stable electrocatalysts for the hydrogen evolution reaction(HER)in acidic electrolytes is a significant challenge.In this work,homogeneous Pt nanodendrites(Pt NDs)with a PtIr shell were successfully synthesized by a two-step wet chemical method.This open three-dimensional(3D)dendritic structure exhibited exceptional electrocatalytic characteristics,exposing as many active sites as feasible.Furthermore,by alloying Ir with Pt on the surface,catalytic activity was greatly enhanced while ensuring extremely high stability.Iridium surface-enriched platinum nanodendritic catalysts(Pt@PtIr NDs)outperformed the control samples and the commercial catalysts.In acidic HER test,Pt@PtIr NDs had a lower overpotential(22 mV)than Pt NDs(26 mV)and commercial Pt/C(31 mV)at 10 mA/cm^(2),and the activity of Pt@PtIr NDs remained consistent even after undergoing a continuous durability test for at least 168 h,which was much superior to the performance of commercial Pt/C(10 h)under identical test conditions.This study revealed that the application of 3D Pt dendritic metal alloys may offer a chance for the development of enhanced electrocatalysts in acidic HER.

Honeycomb-like MoCo alloy on 3D nitrogen-doped porous graphene for efficient hydrogen evolution reaction

An efficient electrocatalyst is indispensable to significantly reduce energy consumption and accelerate the conversion efficiency of water splitting.In this work,the honeycomb-like porous MoCo alloy on nitrogen-doped three-dimensional(3D)porous graphene substrate(Mo_(0.3)Co_(0.7)@NPG)has been synthesized from the annealing of layered double hydroxide(MoCo-LDH@NPG).Especially,the Mo_(0.3)Co_(0.7)@NPG exhibits low hydrogen evolution overpotential of 75 mV(10 mA·cm^(-2))and a Tafel slope of 69.9 mV·dec^(-1),which can be attributed to highly conductive NPG substrate,the unique nanostructure and the synergistic effect of Mo and Co.Moreover,the Mo_(0.3)Co_(0.7)@NPG can maintain the original morphology and high catalytic activity after 50-h stability test.This work proposes a general strategy to synthesize a multi-element alloy on conductive substrates with high porosity for electrocatalytic reaction.

Porous Nickel-Molybdenum Phosphide Alloy Electrodes for Alkaline Hydrogen Evolution Reaction at the High-Current Density

Alkaline water electrolysis is a practical route for large-scale green hydrogen production to assist decarbonization,whereby carbon dioxide emissions are limited.However,the use of this process in hydrogen evolution reaction(HER)is hampered by the alkaline solution,which leads to slow H_(2)O dissociation kinetics,especially when nickel–molybdenum(NiMo)alloy catalysts are utilized;thus,an improvement of this approach for effective HER activity is desirable.In this work,a porous phosphide NiMo-based(NiMoP)alloy electrode catalyst was engineered using a multistep electrodeposition method.Various experiments,combined with theoretical calculations,confirmed that the phosphide incorporation in the NiMo alloys promoted alkaline HER performance at a high current density of 1000 mA cm^(−2)with the potential−0.191 V.The evaluation of the effect of electrodeposition current density on HER performance revealed that the P content indeed positively impacted the accompanying alkaline HER performance,attributable to phosphide contribution in the electron reconstruction.Density functional theory(DFT)calculations demonstrated that the P atom promoted the loss of Mo electrons and hindered Ni from gaining electrons.This charge reconstruction allowed the optimization of the H^(*)adsorption,contributing to a stronger H_(2)O adsorption and encouraging H-OH^(*)bond breakage.Our current approach may provide the possibility of designing high-performance alkaline HER electrodes at high current density.

Electrodeposition:Synthesis of advanced transition metal-based catalyst for hydrogen production via electrolysis of water

Developing lower-cost and higher-effective catalyst to support hydrogen(H_(2))production by electrochemical water-splitting has been recognized as a preferred strategy to drive the clean energy utilization.As a credible technology for the synthesis of functional materials,electrodeposition has attracted widespread attention,especially suitable for non-noble transition metal-based catalysts(TMCs).Recently,lots of researchers have been devoted to this hot research direction with plentiful achievements,however,a comprehensive review towards this area is still missing.Hence,we summarize the past research progress,presents the technical characteristics of electrodeposition from the viewpoint of fundamental theory and influence factors for the electrochemical deposition behavior,and introduce its application in various of TMCs with versatile nanostructures and compositions.Except a deeper and more comprehensive cognition of electrodeposition,we further discuss the catalyst’s optimized hydrogen evolution reaction(HER),oxygen evolution reaction(OER)performance as well as overall water splitting that combined with the synthetic process.Finally,we conclude the technical advantages towards electrodeposition,propose challenge and future research directions in this promising field.This timely review aims to promote a deeper understanding of effective catalysts obtained via electrodeposition strategy,and provide new guidance for the design and synthesis of future catalysts for hydrogen production.

Influence of sodium silicate on manganese electrodeposition in sulfate solution

The influences of sodium silicate on manganese electrodeposition in sulfate solution were investigated. Manganese electrodeposition experiments indicate that a certain amount of sodium silicate can improve cathode current efficiency and initial pH 7.0?8.0 is the optimized pH for high cathode current efficiency. The analyses of scanning electron microscopy (SEM) and X-ray diffraction (XRD) indicate the compact morphology and nanocrystalline structure of electrodeposits. X-ray photoelectron spectrometry (XPS) analysis shows that the elements of Mn, Si and O exist in the deposit. The solution chemistry calculations of sulfate electrolyte and sodium silicate solution indicate that species of Mn2+, MnSO4, Mn(SO4)2?2 , Mn2+, MnSiO3, Mn(NH3)2+, SiO32?and HSiO3? are the main active species during the process of manganese electrodeposition. The reaction trend between Mn2+ and Si-containing ions is confirmed by the thermodynamic analysis. In addition, polarization curve tests confirm that sodium silicate can increase the overpotential of hydrogen evolution reaction, and then indirectly improve the cathode current efficiency.

Surface cleaned Cu_(x)Pd_(y)alloy:Synthesis and their superior performances in hydrogen evolution reaction and biosensor

High cost and restricted activity of electrocatalysis are the major challenges for hydrogen generation and biosensors.In this work,we provided a one-pot synthesis of Cu_(x)Pd_(y)alloy nanoparticles(NPs)with controllable atomic ratio and“clean surface”.Benefiting from the preferable d-band structure,the Cu_(62)Pd_(38)NPs exhibited a lower overpotentials in the hydrogen evolution reaction(HER)over the full pH range.In the acidic media,Cu_(62)Pd_(38)NPs achieved a low overpotential of 28.12 mV for HER,which was 25.73%of Pd NPs.In the neutral solution,the overpotential by Cu_(62)Pd_(38)NPs is only 41.71%for that by uncleaned CuPd NPs.In alkaline media,the overpotential by Cu_(62)Pd_(38)NPs was declined from 38.01 to 20.20 mV after 720 min yielding hydrogen,which was only 53.14%for the initial overpotential.As applied in biosensor,the synergistic effect of Cu and Pd accelerated the kinetics of electrocatalytic process,resulting in an enhanced performance.The glucose sensor constructed by Cu_(67)Pd_(33)exhibited a wider detection range up to 100.0 mM.And the sensitivity is 379.4μA/(mM·cm^(2)),which is ca.4.63 and 14.09 folds for that by pure Cu NPs and Pd NPs,respectively.An optimal atomic percent would be conducive to optimize electrocatalytic activity of Cu_(x)Pd_(y)alloy.The volcano plots for Cu_(x)Pd_(y)would open up a new avenue for designing electrocatalysis with rationalized cost and optimized performance.

Self-templating synthesis and structural regulation of nanoporous rhodium-nickel alloy nanowires efficiently catalyzing hydrogen evolution reaction in both acidic and alkaline electrolytes

Highly active and stable electrocatalysts to produce hydrogen through water splitting are crucial for clean energy systems but are still challenging.Herein,a novel self-templating strategy was proposed to synthesize one-dimensional nanoporous RhNi alloy nanowires through combining metallurgical eutectic solidification and microalloying with chemical dealloying.In-situ X-ray diffraction and ex-situ characterizations reveal that the Al matrix served as a template to guide the growth of the Al3(Ni,Rh)nanowires during eutectic solidification of Al-Ni-Rh precursor and was completely removed in the dealloying process.Meanwhile,the nanowire morphology could be well retained and the dealloying of Al_(3)(Ni,Rh)led to the formation of nanoporous RhNi alloy nanowires.The length scale of the RhNi nanowires could be facilely regulated by changing the solidification conditions.More importantly,the RhNi catalysts show excellent electrocatalytic activity and stability towards hydrogen evolution reaction in both acidic and alkaline media,which has been rationalized by density functional theory calculations.

Lattice strain induced by trace Pt single atoms in nickel for accelerating industrial hydrogen evolution

Strategically designing the electrocatalytic system and cleverly inducing strain is an effective approach to balance the cost and activity of Pt-based electrocatalysts for industrial-scale hydrogen production.Herein,we present a unipolar pulsed electrodeposition(UPED) strategy to induce strain in the Ni lattice by introducing trace amounts of Pt single atoms(SAs)(0.22 wt%).The overpotential decreased by 183 mV at 10 mA cm^(-2) in 1.0 M KOH after introducing trace amounts of Pt_(SAs).The industrial electrolyzer,assembled with Pt_(SAs)Ni cathode and a commercial NiFeO_(x) anode,requires a cell voltage of 1.90 V to attain 1 A cm^(-2) of current density and remains stable for 280 h,demonstrating significant potential for practical applications.Spherical aberration corrected scanning transmission electron microscopy(AC-STEM),X-ray absorption(XAS),and geometric phase analysis(GPA) indicate that the introduction of trace amounts of Pt SAs induces tensile strain in the Ni lattice,thereby altering the local electronic structure and coordination environment around cubic Ni for enhancing the water decomposition kinetics and fundamentally changing the reaction pathway.The doping-strain strategy showcases conformational relationships that could offer new ideas to construct efficient hydrogen evolution reaction(HER) electrocatalysts for industrial hydrogen production in the future.

Electronic Communication Between Co and Ru Sites Decorated on Nitrogen-Doped Carbon Nanotubes Boosting the Alkaline Hydrogen Evolution Reaction

Designing highly efficient Pt-free electrocatalysts with low overpotential for an alkaline hydrogen evolution reaction(HER)remains a significant challenge.Here,a novel and efficient cobalt(Co),ruthenium(Ru)bimetallic electrocatalyst composed of CoRu nanoalloy decorated on the N-doped carbon nanotubes(CoRu@N-CNTs),was prepared by reacting fullerenol with melamine via hydrothermal treatment and followed by pyrolysis.Benefiting from the electronic communication between Co and Ru sites,the as-obtained CoRu@N-CNTs catalyst exhibited superior electrocatalytic HER activity.To deliver a current density of 10 mA·cm^(-2),it required an overpotential of merely 19 mV along with a Tafel slope of 26.19 mV·dec^(-1)in 1 mol·L^(-1)potassium hydroxide(KOH)solution,outperforming the benchmark Pt/C catalyst.The present work would pave a new way towards the design and construction of an efficient electrocatalyst for energy storage and conversion.

Highly active porous nickel-film electrode via polystyrene microsphere template-assisted composite electrodeposition for hydrogen-evolution reaction in alkaline medium

A highly porous nickel-film electrode with satisfactory mechanical strength was prepared by a facile vertical template-assisted composite electrodeposition method using polystyrene(PS) microspheres templates, with the aim of improving the electrocatalytic activity for the hydrogen-evolution reaction(HER). During the composite electrodeposition process, the hydrophobic PS microspheres were highly dispersed in the electrolyte with the help of a surfactant, and then co-deposited with Ni to form the film electrode. After removing the PS templates by annealing, a porous Ni film containing large amount of uniformly dispersed pores with narrow size distribution was obtained, and then applied as the electrode for the HER in an alkaline medium. As evidenced by the electrochemical analysis, the porous Ni film electrode exhibits higher catalytic activity as compared to a dense Ni film electrode and is superior to a Ni/Ru O2/Ce O2 commercial electrode. The effect of temperature on the catalytic properties of the porous Ni film electrode was also investigated; the activation energy was calculated as 17.26 k J/mol. The enhanced activity toward the HER was attributed to the improved electrochemical surface area and mass transportation facilitated by the high porosity of the synthesized Ni film electrode.

Electrocatalytic characterization of Ni-Fe-TiO_(2) overlayers for hydrogen evolution reaction in alkaline solution

The Ni-Fe-TiO_(2) overlayers on mild steel strips were prepared by electrochemical deposition.The layers were characterized morphologically by confocal laser scanning microscopy and scanning electron microscopy(SEM) coupled with energy-dispersive spectroscopy(EDS)analysis.The layers exhibit a quasi-three-dimensional(3D)morphology in which the crystalline,TiO_(2),is embedded.Electrocatalytic activity of the Ni-Fe-TiO_(2) layers for the hydrogen evolution reaction(HER) was assessed by using pseudo-steady-state polarization curves and electrochemical impedance spectroscopy(EIS) in alkaline solution.The results were compared with the properties of Ni-Fe electrodes and used for determining the mechanism and kinetics of HER.In comparison with Ni-Fe electrodes,the synthesized Ni-Fe-TiO_(2) electrodes present higher catalytic activity for HER due to the increase in the real surface area and high intrinsic elec trocatalytic activity of titanium dioxide.The present study provides valuable insight for exploring practical applications of Ni-based alloys as hydrogen evolution electrodes.

Highly efficient nanoporous CoBP electrocatalyst for hydrogen evolution reaction

Water splitting is an environment friendly and efficient way to produce hydrogen.Highly efficient and low-cost non-noble metal catalysts play an important role in hydrogen evolution reaction(HER).Dealloying is a simple method to prepare three-dimensional self-supporting nanoporous materials without conductive supports and binders.In this work,we prepared self-supporting nanoporous CoBP electrocatalyst by dealloying method.The influence of the synergistic effect of nonmetallic elements on catalytic activity was investigated.The synergistic electronic effect of Co,B and P atoms on the surface optimizes the H atoms desorption and results in superior HER activity.The bi-continuous structure of nanoporous CoBP provides more active area and favors of electron and electrolyte transfer.The nanoporous CoBP with the B/P atomic ratio of 1/3 exhibits low overpotential of 42 mV at 10 mA·cm^(-2),small Tafel slope of 39.8 mV·dec-1 and good long-term stability with no performance decrease for 20 h in alkaline solution.

Pt-Co single atom alloy catalysts: Accelerated water dissociation and hydrogen evolution by strain regulation

The alkaline hydrogen evolution reaction(HER) on Pt-based catalysts is largely limited by the slow water dissociation kinetics. Pt-based single atom alloy catalysts(SAAC) with water dissociation sites have been demonstrated as excellent alkaline HER catalysts. However, the regulation of their activity and stability at the atomic scale is still a great challenge. Herein, the kinetic and stability issues are successfully resolved via engineering the electronic structure of Pt-Co SAAC by Au-induced tensile strain. The atomic dispersion of Co into the Pt shell was confirmed by extended X-ray absorption fine structure and the electronic structure and catalytic HER performance was modulated by the tensile strain induced by the Pt shell thickness. An inverse volcano-type relation between HER activity and surface strain was found.Density functional theory(DFT) calculations reveal that the Au-induced tensile strain on Pt-Co shell can not only boost the adsorption and dissociation kinetics of water at Co site by upshifting the dband and promoting the electron transfer, but also downshift the d-band center of Pt in Pt-Co shell, leading to optimized H* adsorption/desorption. The champion catalyst provides an overpotential of only 14 m V at the current density of 10 mA cm^(-2). This work not only provides an effective strategy for the construction of single-atom alloy electrocatalysts for high performance toward alkaline HER but also sheds light on the understanding of the reaction mechanism at the atomic level.