Metal Electrocatalysts For Hydrogen Evolution Reaction Research Articles

Interface regulation of Zr-MOF/Ni2P@nickel foam as high-efficient electrocatalyst for pH-universal hydrogen evolution reaction

Currently, the development of economical and effective non-noble metal electrocatalysts is vital for advancing hydrogen evolution reaction (HER) and enabling its widespread applications. The customizable pore structure and enormous surface area of metal–organic frameworks (MOFs) have made them to become promising non-noble metal electrocatalysts for HER. However, MOFs have some challenges, including low conductivity and instability, which can result in them having high overpotentials and slow reaction kinetics in electrocatalytic processes. In this work, we present an innovative approach for synthesizing cost-effective and high-efficient Zr-MOF-derived pH-universal electrocatalysts for HER. It entails creating the interfaces of the electrocatalysts with suitable proportions of phosphide nanostructures. Zr-MOF/Ni2P@nickel foam (NF) electrodes with interface regulated by Ni2P nanostructures were successfully developed for high-efficient pH-universal HER electrocatalysts. The presence of Ni2P nanostructures with abundant active sites at the Zr-MOFs@NF interfaces boosted the electronic conductivity and local charge density of the hybrid electrocatalysts. This helped to improve their reaction kinetics and electrocatalytic activity. By optimizing the Ni2P amount, Zr-MOF/Ni2P@NF demonstrated impressive stability and superior HER activities, with a low overpotential of 149 mV (acidic electrolytes) and 143 mV (alkaline electrolytes) at 10 mA cm−2. The proven strategy in this work can be expanded to many types of MOF-based materials for wider practical applications.

Innovative Morphology Control Method: Modulating Metal Ratios in NixCoP@NF for Hydrogen Evolution Reaction

AbstractThe use of non‐precious metal materials for catalyzing the hydrogen evolution reaction (HER) holds significant importance for the widespread application of new energy technologies. In this study, we prepare a novel foam nickel (NF) supported NixCoP (NixCoP@NF) nanocrystal through a one‐pot hydrothermal method and high‐temperature phosphorization, involving a straightforward process. Innovatively, we achieve morphology control of NixCoP@NF by altering the Ni : Co ratio to maximize its active surface area. The resulting ′petal‐like′ Ni0.5CoP@NF nanostructure exhibits high activity and long‐term durability in an alkaline medium (1 M KOH), with an overpotential of 58 mV at a current density of 10 mA ⋅ cm−2, a Tafel slope of 60.82 mV ⋅ dec−1, and demonstrates lower impedance compared to most non‐precious metal HER electrocatalysts. Furthermore, the variation in activation energy (Ea) reflects the thermodynamic advantages during the electrolysis process. This work offers a new approach for the development of simple and cost‐effective HER catalysts.

Spatial Relation Controllable Di-Defects Synergy Boosts Electrocatalytic Hydrogen Evolution Reaction over VSe2 Nanoflakes in All pH Electrolytes.

Defect engineering of transition metal dichalcogenides (TMDCs) is important for improving electrocatalytic hydrogen evolution reaction (HER) performance. Herein, a facile and scalable atomic-level di-defect strategy over thermodynamically stable VSe2 nanoflakes, yielding attractive improvements in the electrocatalytic HER performance over a wide electrolyte pH range is reported. The di-defect configuration with controllable spatial relation between single-atom (SA) V defects and single Se vacancy defects effectively triggers the electrocatalytic HER activity of the inert VSe2 basal plane. When employed as a cathode, this di-defects decorated VSe2 electrocatalyst requires overpotentials of 67.2, 72.3, and 122.3mV to reach a HER current density of 10mAcm-2 under acidic, alkaline, and neutral conditions, respectively, which are superior to most previously reported non-noble metal HER electrocatalysts. Theoretical calculations reveal that the reactive microenvironment consists of two adjacent SA Mo atoms with two surrounding symmetric Se vacancies, yielding optimal water dissociation and hydrogen desorption kinetics. This study provides a scalable strategy for improving the electrocatalytic activity of other TMDCs with inert atoms in the basal plane.

Mechanistic insights into hydrogen evolution reaction on Ni2B(001) facet using first-principle calculations

In this paper, first-principle calculations based on density functional theory (DFT) were used to investigate the performance and mechanism of the hydrogen evolution reaction (HER) on the typical active (001) facet of the novel electrocatalyst Ni2B. There were two types of atomic distribution on the Ni2B (001) surface, namely the B-rich surface and the Ni-rich surface. The investigation of the reaction mechanism revealed that the Volmer-Heyrovsky mechanism was easier to be realized on this Ni2B (001) facet, and the Heyrovsky reaction was the reaction rate-determining step. The Gibbs free energy(ΔGH) on the B-rich surface was - 0.02 eV, which was closer to 0 eV than that on the Ni-rich surface of Ni2B (001). The HER reactivity on the Ni-rich surface was increased by Cr-doping (ΔGH = - 0.01 eV), which indicated that the introduction of other transition metal atoms might effectively increase the HER electrocatalysis activity of Ni2B (001) surface. This work paves a new avenue for exploring efficient and durable non-precious metal electrocatalysts for HER in acidic medium.

Effect of cobalt doping and sugarcane bagasse carbon on the electrocatalytic performance of MoS2 nanocomposites

Conductivity, active sites, and structural stability significantly affect the hydrogen evolution reaction (HER) of non-noble metals catalysts (molybdenum disulfide (MoS2)). Therefore, this work proposed a cobalt (Co) doping strategy, to improve the catalytic activity of MoS2, and MoS2 cum sugarcane bagasse derived carbon conjugate (MoS2-SCBC). The designed Co-doped MoS2 (Co-MoS2) and Co-doped SCBC-MoS2 (Co-MoS2-SCBC) nanosheets can enhance the HER activity in the acid electrolyte. The results showed that Co atoms can replace Mo atoms during the doping process of MoS2 to form covalent doping for MoS2. As a carbon carrier, SCBC did not only enhance the electronic conductivity of MoS2 and stability of the mixed structure, but also they were conducive to the dispersion of MoS2, and the exposure of more edge active sites. In addition, Co-MoS2-0.67-SCBC-0.2 showed improved HER electrochemical activity, with overpotential of 62 mV and a lowest Tafel slope of 53.86 mV dec-1 at 10 mA cm−2. The Cdl value for Co-MoS2-0.67-SCBC-0.2 was about 93.36 mF cm−2. Co-MoS2-0.67-SCBC-0.2 also exhibited high stability under acidic conditions, maintained its activity in more than 2000 cyclic voltammetry scans, and had strong durability after 12 h of 10 mA cm−2 exposure. In conclusion, this work provides a Co atom doping strategy to combine biomass waste with inert MoS2 in producing low-cost and highly active non-noble metal electrocatalysts for HER.

One-Step Template/Solvent-Free Pyrolysis for In Situ Immobilization of CoP Nanoparticles onto N and P Co-Doped Carbon Porous Nanosheets towards High-efficiency Electrocatalytic Hydrogen Evolution.

The search for economical, active and stable electrocatalysts towards the hydrogen evolution reaction (HER) is highly imperative for the progression of water electrolysis technology and related sustainable energy conversion technologies. The delicate optimization of chemical composition and architectural configuration is paramount to design high-efficiency non-precious metal HER electrocatalysts. Herein, we report a one-step scalable template/solvent-free pyrolysis approach for in situ immobilizing uniform CoP nanoparticles onto N and P co-doped carbon porous nanosheets (denoted as CoP@N,P-CNSs hereafter). The simultaneous consideration of architectural design and nanocarbon hybridization renders the formed CoP@N,P-CNSs with plentiful well-dispersed anchored active sites, shortened pathway for mass diffusion, enhanced electric conductivity, and reinforced mechanical stability. As a consequence, the optimized CoP@N,P-CNSs exhibit an overpotential of 115 mV to afford a current density of 10 mA cm-2 , small Tafel slope of 74.2 mV dec-1 , high Faradaic efficiency of nearly 100 %, and superb long-term durability in an alkaline medium. Given the fabrication feasibility, mass production potential and outstanding HER performance, the CoP@N,P-CNSs may hold great promise for large-scale electrochemical water splitting. More importantly, the explored one-step template/solvent-free pyrolysis methodology offers a feasible and versatile route to fabricate carbon nanosheet-based nanocomposites for diverse energy conversation-related applications.

Co/MoN hetero-interface nanoflake array with enhanced water dissociation capability achieves the Pt-like hydrogen evolution catalytic performance

Developing high-performance electrocatalyst for hydrogen evolution reaction (HER) is paramount for hydrogen economy. Molybdenum-based nitrides (MoNx) are promising HER catalysts in alkaline condition; however, the performance is greatly limited by the weak water dissociation capacity to form adsorbed H* from H2O, which is crucial but long ignored. Herein, we develop a new strategy to enhance the water dissociation capacity of MoN by forming Co/MoN hetero-interface nanoflake array. The electronic structure of MoN can be effectively modulated by the electron transfer occurred at the Co/MoN hetero-interface. Co/MoN nanoarray also possesses a significantly increased electrochemically active surface area. Co/MoN nanoarray thus exhibits remarkable HER activity with an overpotential of 132 mV to reach 100 mA/cm2, which is among the best non-noble metal HER electrocatalysts in alkaline solution. The very low energy barrier of -0.04 eV for water dissociation on Co/MoN calculated by density functional theory confirms the strong water dissociation capability.

Modulation of Volmer step for efficient alkaline water splitting implemented by titanium oxide promoting surface reconstruction of cobalt carbonate hydroxide

The sluggish water dissociation (Volmer step) is a rate-limiting step slowing down alkaline hydrogen evolution reaction (HER), and therefore hinders the efficient industrial production of clean hydrogen resource. In this work, we report that the Volmer step can be facilitated by in-situ surface reconstruction on a composite between cobalt carbonate hydroxide and titanium oxide (TiO 2 @CoCH), and the resultant activated structure turns to be a highly efficient electrocatalyst for alkaline HER. Experimental characterization and density functional theory calculation evidence that under HER potential the smooth TiO 2 @CoCH surface is roughened and Co interstitial defects in TiO 2 are formed, which are energetically favorable for Volmer step. The activated composite exhibits an overpotential of 99 ± 6 mV for a current density of 20 mA cm −2 and 187 ± 21 mV for 100 mA cm −2 , suggesting that TiO 2 @CoCH is one of promising non-precious metal electrocatalysts for HER in alkaline media. • The combination of two inert component resulted in a highly active electrocatalyst for alkaline hydrogen evolution reaction. • Titanium oxide promoted the surface reconstruction of cobalt carbonate hydroxide during hydrogen evolution reaction. • The Volmer step of hydrogen evolution reaction was significantly promoted after surface reconstruction. • The surface reconstruction of cobalt carbonate hydroxide during hydrogen evolution reaction was evidenced.

Ultrasmall Mo2C in N-doped carbon material from bimetallic ZnMo-MOF for efficient hydrogen evolution

The exploration and development of cost-effective and highly stable electrocatalysts with the highest possible energy efficiency remain a constant pursuit in the catalyst design and synthesis for electrocatalytic hydrogen evolution reaction (HER). In this work, a convenient approach is proposed to synthesize a type of ultrafine Mo2C nanoparticles in average sizes of 3–4 nm embedded in hierarchically porous N-doped carbon material calcined from bimetallic ZnMo-MI (MI = 2-methylimidazole) is obtained at 1000 °C, denoted as ZnMo-MI-1000. First of all, the crystalline hybrid metal-organic framework of ZnMo-MI is fabricated from zeolitic imidazolate framework of Zn-MI precursors via solvothermal reaction, in which the conversion from Zn-MI to ZnMo-MI occurs gradually over time. After calcination, the as-obtained ZnMo-MI-1000 sample shows a satisfying HER performance with the small overpotential of 83.0 mV in 0.5 M H2SO4 and 100.1 mV in 1.0 M KOH to reach a current density of 10 mA cm−2, which is attributed to ultrasmall Mo2C, Mo and N-doped graphitic carbon matrix. The multiporous network of ZnMo-MI-1000 can provide continuous mass transportation with a minimal diffusion resistance that produce effective electrocatalytic kinetics in both acidic and alkaline media, which is utilized as a highly active and durable nonprecious metal electrocatalyst for HER.

Ni@Ni3C Nanochain-SWCNT Composite with Comparable Electrocatalysis of Benchmark Pt/C for Hydrogen Evolution Reaction

Developing robust and low-cost electrocatalysts for efficient hydrogen evolution reaction (HER) through facile methods is of great significance to the energy and environment sustainability. Herein, a simple one-pot solvothermal method has been developed to synthesize a hybrid material of nickel@nickel carbide (Ni@Ni3C) nanochain embedded in a network of single-walled carbon nanotubes (SWCNTs). The electrochemical experiments indicate that the composite of Ni@Ni3C-SWCNTs has the HER electrocatalytic performance comparable to that of Pt/C in an acidic medium (0.5 M H2SO4). The overpotential to reach a current density of 10 mA cm−2 in 0.5 M H2SO4 is only −74 mV with a Tafel slope of 46.9 mV dec−1. Compared to Ni@Ni3C in the absence of SWCNTs, the enhanced HER performance of Ni@Ni3C-SWCNTs can be attributed to the increased intrinsic activity, improved electronic conductivity, and the electron coupling effect between Ni@Ni3C and SWCNTs. The Ni@Ni3C-SWCNTs composites also show high stability at the overpotential of −0.2 V for 24 h. This work provides guidance for the synthesis of high-performance non-precious metal electrocatalysts for HER.

Facile synthesis of N, S co-doped MoO2@C nanorods as an outstanding electrocatalyst for hydrogen evolution reaction

The fabrication of non-precious metal electrocatalysts for HER (hydrogen evolution reaction) offers a promising approach to tackle the global energy crisis. In this work, a simplistic one-pot fabrication of nitrogen/sulfur co-doped MoO2@C nanorods is synthesized to enhance the electrochemical HER over MoO2@C nanorods. The resultant MoO2@SN-C nanorods consist of MoO2 which is evenly distributed on the rods. Well-controlled experimental fabrication suggests that, the additive amount of sulfanilamide and fumaric acid can resourcefully ease the synthesis of the nanorods and enhanced the electrochemical performance of the fabricated MoO2@SN-C catalysts. These outstanding nitrogen/sulfur co-doped MoO2@C nanorods predicts numerous compensations for electrocatalytic applications and beyond: (1) nitrogen/sulfur co-doped can avert the aggregation of MoO2 nanorods and enhance its high electronic conductivity; (2) the well-dispersed uniformity of MoO2@C nanorods supply plentiful active sites; (3) the enriched crystallinity and active surfaces render active sites and promotes mass electron transfer. Due to these properties, nitrogen/sulfur co-doped MoO2@C nanorods pyrolyzed at the temperature of 825 °C delivers an excellent HER performance with a small overpotential of 83 mV and a small Tafel slope of 78 mV dec−1 in alkaline medium. This study unlocks a novel study-point for the expansion and development of an efficient Mo-based electrocatalysts.

Nanoconical active structures prepared by anodization and deoxidation of molybdenum foil and their activity origin

To improve the surface activity of molybdenum (Mo), a method combining anodizing and deoxidizing annealing in a H2 atmosphere has been proposed to prepare nanocone-structured active Mo foils (NCSAMFs) in this paper. The morphology, composition and catalytic properties of the as-prepared NCSAMF were characterized by field-emission scanning electron microscopy (FESEM), energy dispersive spectrometry (EDS) and electrochemical measurements. Nanoconical structures were generated under a voltage of 20 V for 15 min in the optimized electrolyte, and all the oxygen atoms in the nanoconical structure layer were removed under deoxidation at 650 °C for 3 h in a H2 atmosphere while retaining the nanoconical structure and activity. Compared with the Mo foils treated under different conditions, the NCSAMFs exhibit superior hydrogen evolution reaction (HER) activity with a low onset overpotential of 123 mV and a Tafel slope of 96 mV dec−1, indicating that the NCSAMFs possess high activity and outstanding long-term stability in acidic media. Therefore, the NCSAMFs prepared in this paper are promising transition metal HER electrocatalysts and serve as active matrix materials for Mo-based materials. In addition, the surface energies of the NCSAMF and the Mo foils without nanotreatment were calculated at the atomic and mesoscopic scales, respectively, to provide more insights into the origin of the studied process, and the calculation results demonstrate that the high activity of NCSAMFs is mainly derived from the increase in Mo crystal surface area with high surface energy caused by the nanotreatment and the corresponding increase in the amount of active sites.

Hydrogen evolution reaction in full pH range on nickel doped tungsten carbide nanocubes as efficient and durable non-precious metal electrocatalysts

Design of novel inexpensive non-precious metal electrocatalysts to replace Pt based electrocatalysts for wide pH range hydrogen evolution reaction (HER) still remains great challenges and opportunities, for globally sustainable supply of clean hydrogen. Ni doped tungsten carbide nanocubes supported on Ni foam (W1-xNixC NCs/NF) synthesized via a hydrothermal-carbonization methods is reported. W1-xNixC NCs/NF electrocatalysts exhibit excellent catalytic performance with overpotentials lower than 50 mV in both acidic, alkaline and neutral medium. Meanwhile, large electrochemical surface area and better conductivities of W1-xNixC NCs/NF electrocatalysts are deemed in favour of its efficient catalytic properties. Moreover, the electrocatalysts show superior stability in wide pH range. It is believed that the present work provides a novel strategy for designing low-cost and efficient pH universal non-precious metal electrocatalysts for HER.

Regulating the electronic structure of CoMoO4 microrod by phosphorus doping: an efficient electrocatalyst for the hydrogen evolution reaction.

It is of extreme importance to design efficient electrocatalysts for hydrogen evolution reaction (HER), which is considered as a promising approach to provide efficient and renewable clean fuel (hydrogen). Tuning the electronic structure through heteroatom doping demonstrates one of the most effective strategies to promote the electrocatalytic performance of HER. Herein, phosphorus-doping modulation is utilized to fabricate monoclinic P-CoMoO4 with optimized electron structure supported on nickel foam (P-CoMoO4/NF) for alkaline HER via a facile hydrothermal method, followed by low-temperature phosphidation. Notably, P-CoMoO4/NF shows outstanding electrocatalytic performance for HER in 1 M KOH with a low overpotential of 89 mV at 10 mA cm-2, a remarkable Tafel slope value of 59 mV dec-1, and excellent 24 h-long stability. The excellent catalyst activity and stability merits of P-CoMoO4/NF are comparable to the reported highly efficient non-precious metal HER electrocatalysts and could be applied as a powerful electrocatalyst in water electrolysis. This work provides a superior synthesis strategy for the effective design and rational fabrication of low-cost, highly active, and highly stable non-precious metal HER electrocatalysts for electricity-to-hydrogen applications.

Flower-like MOF-derived Co–N-doped carbon composite with remarkable activity and durability for electrochemical hydrogen evolution reaction

Electrochemical hydrogen evolution reaction (HER) is one of the most economical, sustainable, and attractive methods to produce hydrogen. Contemporarily, it is still a challenge to develop low-cost catalysts with high activity and durability for HER. Herein, we report a simple strategy to develop a Co–N-doped carbon electrocatalyst derived from a new cobalt metal-organic framework (MOF). The new flower-like 2D→3D MOF {[Co(BIPA)(5-OH-bdc)](DMF)}n (1) was constructed based on bis(4-(1H-imidazol-1-yl)phenyl)amine (BIPA) and 5-hydroxyisophthalic acid (5-OH-H2bdc). After that, the Co–N-doped carbon composite Co-MOF-800 was prepared via calcination of MOF 1. Interestingly, Co-MOF-800 exhibited excellent electrocatalytic activity and durability for HER. The onset potential (0.12 V) and Ej=10 value (0.193 V) of the Co-MOF-800 electrode were comparable to that of the most active non-precious metal HER electrocatalysts derived from other MOFs. The HER performance of Co-MOF-800 was stable without degradation even after long-term cycling.

Facile construction of N-doped Mo2C@CNT composites with 3D nanospherical structures as an efficient electrocatalyst for hydrogen evolution reaction

In this study, we synthesized nitrogen-doped Mo2C@carbon nanotube (N-Mo2C@CNT) composites via a facile one-pot method of solvothermal followed by calcination. The SEM and TEM results of N-Mo2C@CNT composites show that the sphere-shaped N-Mo2C is covered by CNTs. In addition, the electrocatalytic performances of the as-obtained N-Mo2C@CNT composites were examined towards the hydrogen evolution reaction (HER) in acidic media. It is revealed that the N-Mo2C@CNT composite with optimum content of CNTs (30 mg) exhibits an excellent catalytic activity with less overpotential of 183 mV at 10 mA cm−2 and smaller Tafel slope of 73.95 mV dec−1 as compared with pure Mo2C. Furthermore, it has a good cycling stability after 1000 cycles. This enhanced activity due to the creation of more active sites, large specific surface area by better synergistic effect between the N-Mo2C and CNT. Consequently, the N-Mo2C@CNT composite is a viable alternative to the noble metal electrocatalysts for HER.

Stabilizing and Activating Metastable Nickel Nanocrystals for Highly Efficient Hydrogen Evolution Electrocatalysis

Exploring high-performance and cost-efficient electrocatalysts with unusual metastable phase offers opportunities for improving the electrochemical hydrogen generation, while it remains a great challenge to achieve them with desirable activity and stability. Herein, we report that the doping engineering in a metastable, hexagonal-close-packed nickel (hcp Ni) electrocatalyst is a largely unrevealed yet important factor in achieving an extremely active and stable electrocatalyst toward alkaline hydrogen evolution reaction (HER). Theoretical predications and experimental results suggest that, while the stability of metastable hcp Ni electrocatalyst can be largely improved via the manganese (Mn) doping due to the lower formation energy and lattice stabilization, the MnO/hcp Ni surface promotes the HER via intrinsic favorable H2O adsorption and fast water dissociation kinetics. Consequently, the Mn-doped hcp Ni electrocatalyst shows a small overpotential of 80 mV at 10 mA/cm2 and a low Tafel slope of 68 mV/dec. The result is even approaching that of the commercial Pt/C, being one of the best reported non-noble metal HER electrocatalysts in alkaline media. Under long-term chronopotentiometry measurement, such electrocatalyst can endure at least 10 h with negligible activity decay and structure change. The present work demonstrates the dimension in boosting the electrocatalysis by doping engineering of metastable electrocatalysts.

Unique Hierarchical Mo2C/C Nanosheet Hybrids as Active Electrocatalyst for Hydrogen Evolution Reaction.

A facile and effective pyrolysis stratagem is proposed for the synthesis of hierarchical Mo2C/C nanosheet hybrids with sodium chloride (NaCl) crystals as a template. Large numbers of well-dispersed sheet-like Mo2C nanoparticles with the thickness of about 20 nm were anchored on the surface of carbon nanosheets. Benefiting from the ideal synergistic catalytic effect between the highly active sheet-like Mo2C nanoparticles and the conductive graphitic carbon, and strong charge transfer ability, the unique hierarchical sheet-like structure of Mo2C/C hybrids demonstrated excellent hydrogen evolution reaction (HER) performance in both alkaline and acid medias with small overpotential (125 mV for 10 mA cm-2 in 1 M KOH and 180 mV for 10 mA cm-2 in 0.5 M H2SO4) and remarkable stability, which is comparable to most reported non-noble metal HER electrocatalysts. With the simplicity and low-cost of the synthetic approach, the strategy presented here can be extendable to the preparation of other transition metal-based/carbon nanosheet hybrids for versatile applications.

NiSe2 nanoparticles embedded in carbon nanowires as highly efficient and stable electrocatalyst for hydrogen evolution reaction

Clean hydrogen energy through water splitting via hydrogen evolution reaction (HER) has attracted much interests. It is significant and urgent to search for low-cost non-noble metal electrocatalysts for highly efficient and stable HER. Herein, for the first time, we present a facile and cost-effective hydrothermal and selenization strategy to synthesize NiSe2 nanoparticles embedded in carbon nanowires (NiSe2/C NWs). As a HER electrocatalyst, the NiSe2/C NWs hybrid delivers outstanding catalytic performance with a very low Tafel slope of 38.7mVdec−1, a small onset potential of ∼−144mV (vs RHE), and a high cathode current density of 33mAcm−2 at −250mV (vs RHE). Moreover, it also exhibits excellent long-term stability of NiSe2/C NWs even after 2000 voltammetric sweeps. The superior HER performance of NiSe2/C NWs is attributed to its unique structure constructed by ultrafine NiSe2 nanoparticles homogenously embedded in highly conductive carbon nanowires, which can not only provide abundant HER active sites, but also enhance the conductivity between the nanoparticles. It suggests that NiSe2/C NWs hybrid is a promising candidate to replace noble metal electrocatalysts for HER.

A Hydrogen Evolution Reaction Catalyst Using Nickel Phosphides with Mixed Crystalline Structure

Introduction Proton Exchange Membrane (PEM) water electrolysis provides a sustainable solution for the production of hydrogen, and is well suited to couple with the intermittent nature of energy sources such as wind and solar. To spur large-scale commercial application of PEM water electrolysis, more efficient and less expensive non-noble metal electrocatalysts towards the hydrogen evolution reaction (HER) are required. Recently, transition metal phosphides (TMPs) have become the typical representatives of the burgeoning non-noble metal HER electrocatalysts due to that their intrinsic structures meet the criteria of outstanding electrocatalysts. It should be noted that the currently studied TMPs are mainly focusing on improving their HER performance by a series of structural engineering methods [1-3]. To the best of our knowledge, there are very few reports on promoting the intrinsic activity of the TMPs in water electrolysis. In this communication, we reported the scalable synthesis of nickel phosphides with a mixed crystalline structure (referred to as Ni2P&Ni3P) toward HER by a solution-phase reaction. To elucidate the superior catalytic activity of Ni2P&Ni3P, we also explored the preparation of the nickel phosphides in a single crystalline state (referred to as Ni2P) and that in a single amorphous state (referred to as Ni-P) for comparison. Result and DiscussionX-ray diffraction patterns of Ni2P&Ni3P、Ni2P and Ni-P are shown in Fig 1a. The analysis of the diffraction data reveals that both tiny Ni2P nanocrystallines and Ni3P nanocrystallines are observed for Ni2P&Ni3P. As for Ni2P, the Ni3P tiny nanocrystallines are vanished and only the intensive diffraction peaks corresponding to Ni2P are observed. In comparison with the crystalline state nickel phosphides, the Ni-P shows poor crystalline order with a very broad peak. The crystalline structures could take effects on the intermediate reaction of HER. In order to compare the hydrogen desorption ability of the three electrocatalysts, the hydrogen oxidation reaction (HOR) was investigated by LSV (Linear scan voltammetry) at 20 mA cm-2 for 5 min immediately after the hydrogen evolution reaction (HER). As it is shown in Fig 1b, the characteristic mixed crystalline structure is expected to promote the hydrogen desorption ability. Thus, the largest peak current density is obtained with Ni2P&Ni3P. Furthermore, steady state polarization curves of different electrocatalysts were shown in Fig 1c. As expected, the Ni2P&Ni3P shows the best HER activity, and the overpotentials required for Ni2P&Ni3P、Ni2P and Ni-P to produce cathodic current densities of 20 mA cm-2 are 154 mV, 221 mV, 262 mV, respectively. Fig 1 (a) XRD patterns of Ni2P&Ni3P, Ni2P and Ni-P; (b) LSV and (c) Steady-state polarization curves of the three types of prepared catalysts at a scan rate of 1 mV s-1. All the electrochemical characterizations are tested in the mixture of 0.1 M H2SO4 and 0.5 M Na2SO4 at 25 ◦C and atmosphere pressure. Reference[1] Liu P., Rodriguez J. A. Catalysts for Hydrogen Evolution from the [NiFe] Hydrogenase to the Ni2P (001) Surface: The Importance of Ensemble Effect [J]. Journal of the American Chemical Society, 2005,127(42):14871-14878. [2] Popczun E. J., Read C. G., Roske C. W., Lewis S., Schaak R. E. Highly Active Electrocatalysis of the Hydrogen Evolution Reaction by Cobalt Phosphide Nanoparticles [J]. Angewandte Chemie International Edition, 2014,53(21):5427-5430. [3] Liu Q., Pu Z. H., Asiri A. M., Sun X. P. Nitrogen-doped carbon nanotube supported iron phosphide nanocomposites for highly active electrocatalysis of the hydrogen evolution reaction [J]. Electrochim Acta, 2014,149(10):324-329. Figure 1