Recent advances in amorphous metal phosphide electrocatalysts for hydrogen evolution reaction

Hydrogen is a green energy with the long-term sustainability and high energy density. Hydrogen evolution reaction via electrocatalysis is a prospective strategy for green hydrogen. Pt-based electrocatalysts have exhibited excellent electrocatalytic activities on hydrogen evolution reaction. But the scarce and costly Pt limits the application of hydrogen evolution reaction. Therefore, non-Pt/low-Pt electrocatalysts have attracted much research attention. Amorphous metal phosphide electrocatalysts have shown significant electrocatalytic activities on hydrogen evolution reaction for their special long-range disordered but short-/medium-range ordered structures with abundant active sites and adjustable electronic structures. Mechanisms and electrochemical parameters of hydrogen evolution reaction as well as characterization technologies and atomic configurations of amorphous metal phosphides are firstly illustrated in the review. Amorphous monometallic, bimetallic, trimetallic and other multimetallic phosphides were investigated for modulation of electronic structures and active sites by heteroatom incorporation, nanoporous structure and heterostructure construction. The electrocatalytic performances of these amorphous metal phosphides are summarized in the review. Whereas some questions have emerged in recent researches, like atom leaching, uncertain self-constructions and lack of atomic configurations. Therefore, the future perspectives for the development of amorphous metal phosphide electrocatalysts on hydrogen evolution reaction are construction of stable amorphous metal phosphide electrocatalysts, exploration of self-construction mechanism and convenient construction of atomic configurations.     

Engineering biphasic hybrid phosphide nanowires as efficient electrocatalyst for hydrogen evolution reaction: Experimental and theoretical insights

Development of highly efficient and cheap electrocatalysts towards the hydrogen evolution reaction (HER) is of great importance for electrochemical water splitting. Herein, hybrid Cu/NiMo-P nanowires on the copper foam were successfully fabricated via a simple two-step method. The hierarchically structured Cu/NiMo-P exhibits large surface areas and rapid electron transfer ability, leading to enhanced catalytic activity. The as-prepared Cu/NiMo-P electrodes need overpotentials of 34 mV and 130 mV to obtain 10 mA cm^?2 for HER in acidic and alkaline solutions, respectively. Density functional theory (DFT) calculations reveal that the Cu/NiMo-P hybrid has a more thermo-neutral hydrogen adsorption free energy and enhanced charge transfer ability as well.     

Electronic modulation of multi-element transition metal phosphide by V-doping for high-efficiency and pH-universal hydrogen evolution reaction

Developing highly efficient, durable and noble-metal-free electrocatalysts for hydrogen evolution reaction (HER) in a wide pH range is the key to achieve sustainable energy cycle. Modulating the electronic characteristics of catalysts is of great important to enhance their electrocatalytic performance. Herein, we successfully design a self-supported multi-element transition metal phosphide (V-CoP/Ni₂P/NF) electrocatalyst by V-doping and interface engineering. According to DFT calculations, V dopants and the synergistic effect between CoP and Ni₂P can bring optimal hydrogen/water adsorption free energies. Meanwhile, the 3D cross-linked network structure could expose abundant active sites and facilitate ions diffusion/electron transfer. As a result, the V-CoP/Ni₂P/NF catalysts exhibit superior electrocatalytic activities with extremely low overpotentials of 20, 58 and 79 mV to deliver a current density of 10 mA cm^?2 for HER in alkaline, neutral and acidic electrolytes, respectively. Moreover, they also display outstanding long-term stability. This electronic modulation strategy provides a promising pathway for energy-related catalysis processes.     

Quaternary-metal phosphide as electrocatalyst for efficient hydrogen evolution reaction in alkaline solution

Hydrogen evolution reaction (HER) is a critical process in electrocatalytic water splitting for hydrogen production. However, the development of low-cost electrocatalysts for highly efficient HER is still a huge challenge. Hence, we fabricate a multi-metal phosphide on Ni foam, FeCoNiNb_xP, through a facile hydrothermal reaction followed by phosphorization. We find that Nb promotes the formation of metal phosphides, and the main phases of the catalysts with Nb are multiphase phosphides. Importantly, the Nb incorporation significantly improves the HER activity of FeCoNiP. We show that FeCoNiNb_0.3P has the best HER activity, which only requires an overpotential of 78 mV to achieve a current density of 10 mA cm^?2 in 1 M KOH, and demonstrates excellent stability under both constant potential and varied current densities. Our findings show that the multiple-metal compounds are beneficial to the improvement of catalytic activity and provide guidance on the design of novel catalysts for applications.     

Coral-like prussian blue analogues-derived bimetallic phosphide with enhanced electrocatalytic performance for hydrogen evolution reaction

Tailoring the architecture is of great significance for developing and designing highly active non-noble metal-based electrocatalysts for hydrogen evolution reaction (HER). Here, the architecture of the precursor was improved by alkali etching after the introduction of Prussian blue analogue (PBA). The coral-like precursor was transformed into bimetallic phosphide via phosphating. Detailed investigation disclares that the introduction of PBA could dramatically improves the electrochemical surface area of the material, and the abundant active site could be obtained via alkali etching. In addition, the removal of amorphous carbon may be the main reason for the enhanced conductivity.     

Phase transformation of iron phosphide nanoparticles for hydrogen evolution reaction electrocatalysis

Transition metal phosphides have emerged as alternative electrocatalysts for hydrogen evolution reaction (HER) due to their high activity and low cost compared to the conventional HER electrocatalysts such as Pt. However, the dependency of HER activity on different crystal phases is not well-understood. Here, we synthesized iron phosphide nanoparticles with two distinct phases via chemical transformation from iron metal to iron phosphides. During the development of iron phosphide phases by varying the synthesis conditions such as reaction temperature and time, the HER activities of the nanoparticle were examined. The HER activities of the iron phosphide nanoparticles were found to be phase-dependent.     

Ultrathin MoSSe alloy nanosheets anchored on carbon nanotubes as advanced catalysts for hydrogen evolution

The activity of transition metal dichalcogenides (TMD) toward hydrogen evolution reaction (HER) derives from the active sites at the edges, but the basal surface still remain catalytic insert. Herein, ultrathin MoSSe alloy nanosheets array on multiwalled carbon nanotubes (MWCNTs) to form a core shell structure via a simple solvothermal process. These three-dimensional (3D) MoSSe hybrids show a high activity in hydrogen evolution reaction (HER) with a small Tafel slope of 38 mV dec⁻¹ and a low overpotential of 102 mV at 10 mA cm⁻². In addition, their HER activity remains remarkably stable without significant decay after 100 h polarization. Such superior catalytic HER activity springs from the 3D hierarchical heterostructure, which is abundant of catalytic edge sites, and the alloy effect between S and Se, which will create huge defects and strain to form vacancy sites on the basal plane. This strategy may open a new avenue toward the development of nonprecious high-performance HER catalysts.     

In situ modification of Cu substrate enables nickel-copper phosphide nanoarrays for enhanced electrocatalytic hydrogen evolution

Searching for non-noble and high active electrocatalysts with excellent durability for hydrogen evolution reaction (HER) is significant for hydrogen production but remains a grand challenge. Here, we report a low-temperature oxidation strategy to modify copper foam (CF) and successfully built a heterogeneous NiP₂-Cu₃P nanoarray on the modified CF (NiCuP@CF), in which the CF functions as both conductive support and the precursor of the active substances. The resulting catalyst achieves low overpotentials of 113.4 and 266.4 mV to reach the current density of 10 and 100 mA cm^?2 towards HER in alkaline electrolyte, respectively, benefiting from the 3D heterostructure arrays with abundant active sites and excellent conductivity. The open channels formed spontaneously in the 3D arrays allow rapid H₂ bubbles to escape, which enables the catalyst to exhibit remarkable stability for at least 36 h under different current densities. This work presents a facile and economic modification method for Cu substrate, which will provide a good foundation for the subsequent material optimization, not limited to the heterogeneous metal phosphide catalyst toward HER.     

Multilevel N-doped carbon nanotube/graphene supported cobalt phosphide nanoparticles for electrocatalytic hydrogen evolution reaction

Electrochemical water splitting plays an important role in alternative energy studies, since it is highly efficient and environment-friendly. Accordingly, it is an ideal way of providing alternative to meet the urgent need of finding sustainable and clean energy. This study presents the fabrication of CoP attached on multilevel N-doped CNT/graphene (CoP–CNT/NG) hybrids. The multilevel carbon structure can enhance electrical conductivity efficiently and increase the reaction active area immensely. The obtained electrocatalyst exhibits great electronic conductivity (17.8 s cm⁻¹) and HER activity with low overpotential (155 mV at 10 mA cm⁻²), low Tafel slope (69.1 mV dec⁻¹) in 0.5 M H₂SO₄. In addition, the CoP–CNT/NG displays prominent electrochemical durability after 18 h.     

Self-template synthesis of lychee like Mn-doped Co2P yolk-shell spheres for enhanced hydrogen evolution reaction activity

Designing an electrocatalyst for hydrogen production from water splitting that is highly efficient, stable, and free of noble metals is necessary but challenging. The phosphorus compound is considered a viable candidate for producing hydrogen from water split, but its electrocatalytic performance needs further improvement. Herein, we present an easy and straightforward method for constructing Mn-doped Co₂P yolk-shell lychee spheres. The Co nano prisms are used as a self-sacrificing template to conduct an ion exchange reaction with manganese ions, constructing Co oxide yolk-shell spheres with Mn–Co hydroxide nano-blocks. After in-suit phosphating at low temperature, Mn-doped Co₂P with yolk-shell structure and lychee morphology is formed. The Mn-doped Co₂P with an optimized Mn and Co molar ratio (0.125) exhibits excellent hydrogen evolution performance in alkaline and acidic electrolyte. The overpotentials can reach 10 mA cm^?2 at 98 mV and 72 mV, respectively, and the Mn–Co₂P-0.125 catalyst has faster electron transfer efficiency and larger electrochemically active surface area. The experimental results ascertain that doping an appropriate amount of Mn significantly changes the morphology and structure, thereby affecting the exposure of active sites, and modulating the electronic structure around Co₂P. Under the dual regulation of morphology and electronic structure, the electrocatalytic process is accelerated, enhancing its catalytic activity.     

Iron doped mesoporous cobalt phosphide with optimized electronic structure for enhanced hydrogen evolution

We report a self-supporting electrode fabricated by covering iron doped mesoporous cobalt phosphide film on carbon cloth substrate (meso-Fe_xCo_1-xP/CC) for hydrogen evolution reaction (HER). In acidic and alkaline electrolytes, the electrode exhibited excellent catalytic activity and fast kinetics towards the HER, only requiring small overpotentials of 61 mV and 67 mV to drive 10 mA cm^?2, respectively. The superior electrocatalytic activity is attributed to the mesoporous structure with high specific surface area (147.5 m² g^?1) and doping of Fe atom. The mesoporous structure grown on the conductive carbon cloth substrate enables the fully exposure of active sites and the rapid penetration of electrolyte. Additionally, density functional theory (DFT) calculation reveals that the doping of Fe enhances the adsorption of H atoms by shifting the d-band center of Co. Meanwhile, the introduction of Fe lowers the energy barrier for water dissociation, which accelerates the catalytic kinetics in alkaline electrolyte.     

The catalytic performance enhancement of Ni2P electrocatalysts for hydrogen evolution reaction by carbon-based substrates

Combination of catalytic active components with substrates is deemed to be a promising approach to pursue high active and stable catalysts. Wherein, carbon-based materials as a kind of frequently-used substrates are well developed, and thus the different effects of them on catalytic active components deserve investigating and contrasting. In this work, well dispersive and ultrafine Ni₂P nanoparticles supported on N-doped reduced graphene oxide (N-RGO) were synthesized through a facial hydrothermal process and subsequent phosphorization. The prepared Ni₂P/N-RGO demonstrates a superior electrocatalytic activity towards hydrogen evolution reaction (HER) in 0.5 M H₂SO₄ solution with a low onset overpotential (80 mV) and small Tafel slope (93.1 mV dec⁻¹). Additionally, as compared with other representative carbon materials (carbon black (C) and carbon nanotubes (CNTs)) in the perspective of specific surface area (SSA), conductivity and electronic interaction in particular, N-RGO demonstrates a preeminent promotional effect as a substrate of Ni₂P.     

Synthesis and electrochemical study of coinage metal nanodendrites for hydrogen evolution reaction

Herein, we report a facile one-step synthesis route to fabricate the coinage metal nanodendrites (NDs) via a tailored galvanic replacement reaction (GRR). Cu, Ag and Au NDs are directly grown on glassy carbon plate (GCP) from the mixture of their precursor solutions and Zn dust. The formed NDs are uniformly distributed to the substrate and obtained the unique structures with sharp tips and tertiary branches. The electrocatalytic activity of the synthesized NDs towards the hydrogen evolution reaction (HER) is further investigated in 0.5 M H₂SO₄ using linear sweep voltammetry (LSV) and the Tafel slope. The results demonstrate that the nanodendrites formed through the GRR process exhibit greater catalytical activity towards HER in comparison to the polycrystalline Cu, Ag and Au. The prepared Au NDs exhibits the highest catalytic performance with a current density of ?10.68 mA cm^?2 at overpotential of 67 mV and a low Tafel slope of 65 mV dec^?1. The simple and easy synthesis approach, the unique morphology and high electrocatalytic activity and excellent stability make the developed Cu, Ag and Au NDs highly efficient catalysts for green energy and electrochemical applications.     

Recent advances in cobalt disulfide for electrochemical hydrogen evolution reaction

Hydrogen production by water electrolysis is the most promising green hydrogen supply method in the future. Electrocatalytic hydrogen evolution reaction (HER), an essential step in water electrolysis, has received continuous interest for a long time. Noble metal-based electrocatalysts exhibit excellent performance for HER, while their high price, limited reserves, and insufficient durability limit their large-scale applications. Transition metal sulfides (TMSs) have been extensively studied as potential alternative catalysts, among which cobalt disulfide (CoS₂) stands out due to its unique structure, low price, and good electrical conductivity. Although remarkable progress has been made, the catalytic activity and stability of CoS₂ electrode materials themselves are still insufficient for large-scale industrial applications, so effective improvement of the HER catalytic performance of CoS₂ remains the focus of research. In this review, we briefly outline the reaction mechanism of HER, focusing on strategies to improve the catalytic performance of CoS₂, including morphology engineering, carbon materials combination, heteroatom doping, and heterostructure construction. Furthermore, the key challenges and opportunities for CoS₂ electrode materials as an electrocatalytic material for HER are discussed.     

Ni-W nanostructure well-marked by Ni selective etching for enhanced hydrogen evolution reaction

Designing active, stable and affordable electrocatalysts is a promising pathway for fulfilling the mankind's dream of preserving unsustainable fuel sources. Herein, the facile utilization of Romanesco-like and arrow-like nanostructures of Ni-W samples is introduced. Exclusive emphasis is placed on achievement of the unique nanostructure through cost-effective, repeatable and readily accessible two-step techniques, i.e. Ni-W electrodeposition approach followed by etching treatment. Microscopic study was fully utilized for surface morphology and structural investigation. The electrochemical analysis was used to evaluate the electrocatalytic activity and stability. The surface roughness of the Ni-W film electrodeposited by D.C = 90% and etched via acidic solution was up to 93.85, considerably higher than that of the Ni-W electrodeposited by D.C = 20% and without etched Ni-W films (55.36 and 41.51 respectively). Therefore, HER activity was improved with η₁₀ and η₂₀ of 169 and 226 mV vs. RHE, respectively, due to higher effective active surface for H⁺ adsorption. The Tafel slope analysis suggests Volmer mechanism as the HER rate-determining step. The electrochemically active surface area was also enhanced from roughly 2 to 10 cm². In addition, wettability was investigated by a contact angle of less than 65°, which indicates high penetration of electrolyte to the nanostructure. Rapid separation of bubbles on the arrow-like nanostructure of Ni-W films exhibited unstable H₂ bubbles on surface of the electrode.     

MOF-derived cobalt manganese phosphide as highly efficient electrocatalysts for hydrogen evolution reaction

Hydrogen is considered as a viable alternative to traditional fossil fuels. Hydrogen evolution reaction (HER) by electrochemical water splitting is the most reliable and effective way for the sustainable production of pure hydrogen. The design and synthesis of highly active and stable non-noble-metal-based electrocatalysts is the core of the large-scale application of this technology. Herein, peony petal-like CoMnP/NF nanomaterials growing on nickel foam (NF) are prepared via facile hydrothermal and phosphorization methods. The results showed that CoMnP/NF had excellent HER activity in acidic and alkaline media. In 0.5 M H₂SO₄, CoMnP/NF only needed 66.6 mV overpotential to drive the current density of 10 mA cm^?2, with a Tafel slope of 38.8 mV dec^?1. In addition, a particularly low overpotential of 53.9 mV and Tafel slope of 63 mV dec^?1 are required to achieve the same current density in the 1 M KOH electrolyte. Meanwhile, the electrocatalyst showed good stability after 1000 cyclic voltammetry tests and 12 h I-T tests. In the 1 M KOH electrolyte, the current density of 10 mA cm^?2 achieved with only 1.70 V battery voltage, and the electrocatalyst showed excellent stability. The performance of CoMnP/NF can be attributed to the synergistic effect between Co and Mn atoms and the high electrochemical surface area (ECSA). This study provides a valuable strategy for the synthesis of non-precious metals and high-performance catalytic materials.     

Easily-prepared bimetallic metal phosphides as high-performance electrode materials for asymmetric supercapacitor and hydrogen evolution reaction

Transition metal phosphides are very attractive because of the remarkable performance in energy storage and conversion. Herein, a series of bimetallic phosphides are synthesized through a one-step solid-state reaction. The obtained bimetallic phosphides show outstanding properties as supercapacitor electrode materials. Results show that the incorporation of secondary metal into phosphides tunes composition, electronic structure and then the electrochemical performance. And electrochemical properties are closely associated with the secondary metal content. Notably, the obtained NiCoP shows the best performance with 2011 F g⁻¹ at 1 A g⁻¹. And an asymmetric supercapacitor (ASC) based on NiCoP shows energy density of 47.6 W h kg⁻¹, along with 90.5% of capacitance maintained after 10000 cycles. In addition, the NiCoP also possesses great performance toward hydrogen evolution reaction (HER), which displays the lowest potential of 0.221 V vs. RHE and 0.173 V vs. RHE at 10 mA cm⁻² in 0.5 M H₂SO₄ as well as 1.0 M KOH, respectively. The excellent properties may result from the enhanced electrical conductivity, synergistic effects among metal elements and the increased local electrical dipole. The regulation of electronic structure through introduction of secondary metal atom sheds considerable light on realization and preparation of the bimetallic transition metal compounds as electrode materials.     

Exfoliated MoS2 with porous graphene nanosheets for enhanced electrochemical hydrogen evolution

Porous graphene (P-rGO) was synthesized from graphene oxide (GO) via a one-pot calcination method with CO₂ as an activation agent at 800 °C. Due to the special porous structure, the surface area of P-rGO can be increased to ～759 m²/g. The P-rGO was then used as a support to incorporate with chemical exfoliated molybdenum disulfide (MoS₂) for the fabrication of MoS₂/P-rGO composite. Compared to bulk MoS₂, the exfoliated MoS₂ is in the 1T phase with a metallic property and smaller charge transfer resistance, thus has a better activity in electrochemical hydrogen evolution reaction (HER). The HER activity of 1T MoS₂ could be further increased after the combination with P-rGO. The overpotential of 1T MoS₂/P-rGO was only ～130 mV vs. RHE, and the corresponding Tafel slope was ～75 mV Dec^?1. The special porous structure and good electric conductivity of P-rGO decrease the charge transfer resistance of the composite without sheltering too many active sites of MoS₂, thus leading to the enhanced HER activity. As an efficient noble metal free HER catalyst, the 1T MoS₂/P-rGO has great potential for large-scale hydrogen production.     

Magnetic field enhancement of electrochemical hydrogen evolution reaction probed by magneto-optics

External magnetic fields affect various electrochemical processes and can be used to enhance the efficiency of the electrochemical water splitting reaction. However, the driving forces behind this effect are poorly understood due to the analytical challenges of the available interface-sensitive techniques. Here, we present a set-up based on magneto- and electro-optical probing, which allows to juxtapose the magnetic properties of the electrode with the electrochemical current densities in situ at various applied potentials and magnetic fields. On the example of an archetypal hydrogen evolution catalyst, Pt (in a form of Co/Pt superlattice), we provide evidence that a magnetic field acts on the electrochemical double layer affecting the local concentration gradient of hydroxide ions, which simultaneously affects the magneto-optical and magnetocurrent response.     

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.