Molybdenum tungsten hydrogen oxide doped with phosphorus for enhanced oxygen/hydrogen evolution reactions

The development of efficient electrocatalysts for hydrogen and oxygen evolution reactions (HER and OER) is pivotal for advancing cleaner and sustainable fuel production technologies. The conventional electrocatalysts have limited stability and higher overpotentials, and there is demand to explore advanced materials and synthesis methods. In this context, a novel bifunctional electrocatalyst has been devised through the phosphidation of tungsten molybdenum oxide (P-Mo0.69W0.31H0.98O3) at relatively low temperatures. This innovative approach aims to enhance the efficiency of HER and OER while minimizing the overpotential values and maintaining higher stability. Specifically, the individual performance of Mo0.69W0.31H0.98O3 has been significantly boosted by doping it with phosphorus at a low temperature of 300 °C. This doping process results in a unique morphology for the catalyst, leading to a notable improvement in OER/HER performances. P-Mo0.69W0.31H0.98O3 exhibits a potential of 320 mV at 10 mA cm-2 in a KOH electrolyte, demonstrating both high activity and long-term stability. Additionally, P-Mo0.69W0.31H0.98O3 exhibits commendable HER performance, requiring only 380 mV at 100 mA cm-2. This combination of efficient OER and HER performance positions P-Mo0.69W0.31H0.98O3 as representing a significant advancement in the field of electrocatalysis, additionally addressing the fundamental gap by providing stable and hybrid catalyst for various electrochemical devices. Given its cost-effectiveness and exceptional activity, P-Mo0.69W0.31H0.98O3 holds significant potential for advancing the field of electrocatalysis and contributing to the development of cleaner and sustainable fuel production methods.

Transition metal atom M (M = Fe, Co, Cu, Cr) doping and oxygen vacancy modulated M-Ni5P4-NiMOH nanosheets as multifunctional electrocatalysts for efficient overall water splitting and urea electrolysis reaction

It is significant to develop reasonable and efficient hydrogen evolution reaction catalysts to alleviate the energy crisis, yet challenging to produce hydrogen through the electrolysis of water and urea. In this work, the dual control strategy of doping and vacancy creation was used to improve the electrocatalytic performance of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) for the design of a multifunctional catalyst. A series of M-doped-Ni₅P₄/M-doped Ni(OH)₂ (M = Fe, Co, Cu, Cr) hierarchical materials with abundant oxygen vacancies was constructed for the first time by hydrothermal and partial phosphating methods. The Co-doped-Ni₅P₄/Co-doped-Ni(OH)₂ (Co-Ni₅P₄-NiCoOH) exhibited superior performance in HER, OER and urea oxidation reaction (UOR). Moreover, the electrode couple is fitted with two Co-Ni₅P₄-NiCoOH (C-NP-NCOH) electrodes to drive the current density of 10 mA cm^-2; the necessary cell voltage was 1.57 V in 1.0 M KOH with 0.5 M urea for urea electrolysis and water electrolysis required a 1.6 V cell voltage in 1.0 M KOH electrolyte, which is one of the best catalytic activities reported so far. The experimental results suggest that the co-action of Co-doping and oxygen vacancies increases the specific surface area of the material, enhances the electronic conductivity and promotes the exposure of more active sites, thus improving the water splitting and urea electrolysis performances of the catalyst. Density functional theory analysis suggests that Co-Ni₅P₄-NiCoOH displays optimal adsorption energy of water and electrical conductivity, thus optimizing the adsorption/desorption of intermediates.

Flower-like Spherical α-Ni(OH)2 Derived NiP2 as Superior Anode Material of Sodium-Ion Batteries

Transition metal phosphides (TMPs) are promising anode candidates for sodium-ion batteries, due to their high theoretical specific capacity and working potential. However, the low conductivity and excessive volume variation of TMPs during insertion/extraction of sodium ions result in a poor rate performance and long-term cycling stability, largely limiting their practical application. In this paper, NiP₂ nanoparticles encapsulated in three-dimensional graphene (NiP₂ @rGO) were obtained from the flower-like spherical α-Ni(OH)₂ by phosphating and carbon encapsulation processes. When used as a sodium-ion batteries anode material, the NiP₂ @rGO composite shows an excellent cycling performance (117 mA h g^-1 at 10 A g^-1 after 8000 cycles). The outstanding electrochemical performance of NiP₂ @rGO is ascribed to the synergistic effect of the rGO and NiP₂ . The rGO wrapped on the NiP₂ nanoparticles build a conductive way, improving ionic and electronic conductivity. The effective combination of NiP₂ nanoparticles with graphene greatly reduces the aggregation and pulverization of NiP₂ nanoparticles during the discharge/charge process. This study may shed light on the construction of high-performance anode materials for sodium-ion batteries and to other electrode materials.

Cobalt-based heterogeneous catalysts in an electrolyzer system for sustainable energy storage

Nowadays, the production of hydrogen and oxygen focuses on renewable energy techniques and sustainable energy storage. A substantial challenge is to extend low-cost electrocatalysts consisting of earth-abundant resources, prepared by straightforward approaches that display high intrinsic activity compared to noble metals. The expansion of bifunctional catalysts in alkaline electrolytes for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) has become very crucial in recent times. Herein, the recent progress in cobalt-based HER-OER electrocatalysts has been are brushed up and numerous bifunctional cobalt-based catalysts such as cobalt-oxides, phosphides, sulfides, selenides, nitrides, borides, carbides, perovskites, and MOF-based cobalt analogs have been investigated in detail. Specifically, much more attention has been paid to their structural variation, bifunctional activity, overpotential of the overall system, and stability. Cobalt-based catalysts with lower cell voltage, remarkable durability, and unique electronic structures, offer a new perspective in energy-related fields. In recent years, cobalt-based analogs with diagnostic facilities have been introduced due to their electronic structures, tunable d band structures, and tailorable active sites. This perspective also elucidates the present issues, promising ideas, and future forecasts for cobalt-based catalysts. The critical aspects of cobalt-based catalysts and the numerous opportunities, as discussed at the end, can possibly enrich the sustainable energy field.

CoNi-based metal–organic framework nanoarrays supported on carbon cloth as bifunctional electrocatalysts for efficient water-splitting

CoNi-based metal–organic framework (MOF) nanoarrays supported on carbon cloth can be used as an efficient bifunctional electrocatalyst for overall water splitting.

The one-step electrodeposition of nickel phosphide for enhanced supercapacitive performance using 3-mercaptopropionic acid

TMPs have received considerable attention for various applications, including the water splitting reaction (hydrogen evolution reaction and oxygen evolution reaction), methanol oxidation, the oxygen reduction reaction, rechargeable batteries, and supercapacitors.

Bifunctional NiFe layered double hydroxide@Ni3S2 heterostructure as efficient electrocatalyst for overall water splitting

The tailored construction of non-noble metal bifunctional electrocatalysts for high-efficiency oxygen/hydrogen evolution reactions (OER/HER) is vital for the development of electrochemical energy conversion. Herein, we report a powerful combined wet chemical method to fabricate a novel binder-free NiFe layered double hydroxide@Ni₃S₂ (NiFe LDH@Ni₃S₂) heterostructure as an efficient bifunctional electrocatalyst for overall water splitting. The hydrothermal-synthesized NiFe LDH nanosheets are uniformly coated on the Ni₃S₂ nanosheet skeleton forming 3D porous heterostructure arrays. By virtue of its synergistic advantages, including its binder-free characteristics, increased catalysis sites and structural stability, the as-obtained NiFe LDH@Ni₃S₂/NF electrode exhibits low overpotentials of 184 and 271 mV at 20 mA cm^-2 for HER and OER in 1 M KOH, respectively. Notably, a low operation potential of 1.74 V at a current density of 20 mA cm^-2 is achieved for overall water splitting with a stable cycling life. In addition, the intimate composite structure and sensitive interface of NiFe LDH@Ni₃S₂ are responsible for the good electrocatalytic activity with a low Tafel slope, fast reaction kinetics and high stability. The versatile fabrication protocol and heterostructure interface engineering provide a new way to construct other bifunctional and cost-effective electrocatalysts for electrocatalysis.

Recent Trends in Synthesis and Investigation of Nickel Phosphide Compound/Hybrid-Based Electrocatalysts Towards Hydrogen Generation from Water Electrocatalysis

Sustainable and high performance energy devices such as solar cells, fuel cells, metal-air batteries, as well as alternative energy conversion and storage systems have been considered as promising technologies to meet the ever-growing demands for clean energy. Hydrogen evolution reaction (HER) is a crucial process for cost-effective hydrogen production; however, functional electrocatalysts are potentially desirable to expedite reaction kinetics and supply high energy density. Thus, the development of inexpensive and catalytically active electrocatalysts is one of the most significant and challenging issues in the field of electrochemical energy storage and conversion. Realizing that advanced nanomaterials could engender many advantageous chemical and physical properties over a wide scale, tremendous efforts have been devoted to the preparation of earth-abundant transition metals as electrocatalysts for HER in both acidic and alkaline environments because of their low processing costs, reasonable catalytic activities, and chemical stability. Among all transition metal-based catalysts, nickel compounds are the most widely investigated, and have exhibited pioneering performances in various electrochemical reactions. Heterostructured nickel phosphide (Ni_xP_y) based compounds were introduced as promising candidates of a new category, which often display chemical and electronic characteristics that are distinct from those of non-precious metals counterparts, hence providing an opportunity to construct new catalysts with an improved activity and stability. As a result, the library of Ni_xP_y catalysts has been enriched very rapidly, with the possibility of fine-tuning their surface adsorption properties through synergistic coupling with nearby elements or dopants as the basis of future practical implementation. The current review distils recent advancements in Ni_xP_y compounds/hybrids and their application for HER, with a robust emphasis on breakthroughs in composition refinement. Future perspectives for modulating the HER activity of Ni_xP_y compounds/hybrids, and the challenges that need to be overcome before their practical use in sustainable hydrogen production are also discussed.

Catalytically Active Sites on Ni5P4 for Efficient Hydrogen Evolution Reaction From Atomic Scale Calculation

Ni₅P₄ has received considerable attention recently as a potentially viable substitute for Pt as the cathode material for catalytic water splitting. The current investigation focuses on theoretical understandings of the characteristics of active sites toward water splitting using first-principle calculations. The results indicate that the activity of bridge NiNi sites is highly related on the bond number with neighbors. If the total bond number of NiNi is higher than 14, the sites will exhibit excellent HER performance. For the top P sites, the activity is greatly affected by the position of coplanar atoms besides the bond number. Data of bond length with neighbors can be used to predict the activity of P sites as reviewed by machine learning. Partial density of state (PDOS) analysis of different P sites illustrates that the activity of P sites should form the appropriate bond to localize some 3p orbits of the P atoms. Bond number and position of neighbors are two key parameters for the prediction of the HER activity. Based on the current work, most of the low-energy surfaces of Ni₅P₄ are active, indicating a good potential of this materials for hydrogen evolution reactions.

Hyperbranched Co2P nanocrystals with 3D morphology for hydrogen generation in both alkaline and acidic media

Hyperbranched Co2P nanocrystals with three-dimensional structure have successfully been synthesized by a facile one-step wet-chemical method. The hyperbranched Co2P are consisted of a large number of nanofilaments. The crystal splitting should be responsible for the formation of this structure. Catalytic performances measurements toward hydrogen evolution reaction for the obtained hyperbranched Co2P nanocrystals demonstrate a small overpotential of 100 mV at current density of 10 mA cm-2, with a Tafel slope of 67 mV dec-1 in 1 M KOH. Durability tests show that slight catalytic activity fading occurs after 2000 CV cycles or 22 h chronoamperometric testing. In addition, the hyperbranched Co2P also perform well in 0.5 M H2SO4 with a low overpotential of 107 mV at 10 mA cm-2 and a Tafel slope of 69 mV dec-1. This facile method provides a strategy for the preparation of low-cost metal phosphide electrocatalysts for hydrogen evolution in both alkaline and acidic media.

Interfacial Electron Transfer of Ni2 P-NiP2 Polymorphs Inducing Enhanced Electrochemical Properties

Heterointerface engineering can be used to develop excellent catalysts through electronic coupling effects between different components or phases. As one kind of promising Pt-free electrocatalysts for hydrogen evolution reaction (HER), pure-phased metal phosphide exhibits the unfavorable factor of strong or weak H*-adsorption performance. Here, 6 nm wall-thick Ni₂ P-NiP₂ hollow nanoparticle polymorphs combining metallic Ni₂ P and metalloid NiP₂ with observable heterointerfaces are synthesized. It shows excellent catalytic performance toward the HER, requiring an overpotential of 59.7 mV to achieve 10 mA cm^-2 with a Tafel slope of 58.8 mV dec^-1 . Density functional theory calculations verify electrons' transfer from P to Ni at the heterointerfaces, which decreases the absolute value of H* adsorption energy and simultaneously enhance electronic conductivity. That is, the heterojunctions balance the metallic Ni₂ P and the metalloid NiP₂ to form an optimized phosphide polymorph catalyst for the HER. Furthermore, this polymorph combination is used with NiFe-LDH nanosheets to form an alkaline electrolyzer. It shows highly desirable electrochemical properties, which can reach 10 mA cm^-2 in 1 m KOH at 1.48 V and be driven by an AAA battery with a nominal voltage of 1.5 V. The work about interfacial charge transfer might provide an insight into designing excellent polymorph catalysts.

A self-supported amorphous Ni-P alloy on a CuO nanowire array: an efficient 3D electrode catalyst for water splitting in alkaline media

Energy-efficient electrochemical water splitting is one important way to produce hydrogen fuel but still faces many challenges. In this communication, we report that an amorphous Ni-P alloy shell electrodeposited on a CuO nanowire array supported on copper foam (CuO@Ni-P NA/CF) can be used for efficient water splitting in alkaline media. As a 3D catalytic electrode, it exhibits excellent activity both for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) with overpotentials of 106 mV for HER and 275 mV for OER to achieve a current density of 30 mA cm^-2 in 1.0 M KOH. This bifunctional electrode enables a high-performance alkaline water electrolyzer to achieve a current density of 30 mA cm^-2 at a cell voltage of 1.71 V.

Self-Supported Ternary Ni-S-Se Nanorod Arrays as Highly Active Electrocatalyst for Hydrogen Generation in Both Acidic and Basic Media: Experimental Investigation and DFT Calculation

In this study, a novel three-dimensional self-supported ternary NiS-Ni₉S₈-NiSe nanorod (NR) array cathode has been successfully in situ constructed by a two-step hydrothermal route. When applied to hydrogen evolution, the synthesized NiS-Ni₉S₈-NiSe-NR electrode demonstrates optimized electrocatalytic activity and long-term durability, only requiring overpotentials as low as 120 and 112 mV to drive 10 mA cm^-2 for hydrogen evolution reaction in 0.5 M H₂SO₄ and 1.0 M KOH, respectively. Density functional theory calculation reveals that after Se doping Se 3d orbitals are bonded to Ni 3d orbitals and S p orbitals near Fermi level, attesting a significant electron transfer between nickel and selenium atoms. The success of enhancing the electrocatalytic performance via introducing the Se dopant holds great promise for the potential optimization of other transition-metal compounds in highly efficient electrochemical water splitting for large-scale hydrogen production.

Controlled Electrodeposition Synthesis of Co-Ni-P Film as a Flexible and Inexpensive Electrode for Efficient Overall Water Splitting

Synthesis of highly efficient and robust catalysts with earth-abundant resources for overall water splitting is essential for large-scale energy conversion processes. Herein, a series of highly active and inexpensive Co-Ni-P films were fabricated by a one-step constant current density electrodeposition method. These films were demonstrated to be efficient bifunctional catalysts for both H₂ and O₂ evolution reactions (HER and OER), while deposition time was deemed to be the crucial factor governing electrochemical performance. At the optimal deposition time, the obtained Co-Ni-P-2 catalyst performed remarkably for both HER and OER in alkaline media. In particular, it requires -103 mV overpotential for HER and 340 mV for OER to achieve the current density of 10 mA cm^-2, with corresponding Tafel slopes of 33 and 67 mV dec^-1. Moreover, it outperforms the Pt/C//RuO₂ catalyst and only needs -160 mV (430 mV) overpotential for HER (OER) to achieve 200 mA cm^-2 current density. Co-Ni-P electrodes were also conducted for the proof-of-concept exercise, which were proved to be flexible, stable, and efficient, further opening a new avenue for rapid synthesis of efficient, flexible catalysts for renewable energy resources.

Electrocatalytic hydrogen evolution reaction activity comparable to platinum exhibited by the Ni/Ni(OH)2/graphite electrode

Electrochemical dual-pulse plating with sequential galvanostatic and potentiostatic pulses has been used to fabricate an electrocatalytically active Ni/Ni(OH)₂/graphite electrode. This electrode design strategy to generate the Ni/Ni(OH)₂ interface on graphite from Ni deposits is promising for electrochemical applications and has been used by us for hydrogen generation. The synergetic effect of nickel, colloidal nickel hydroxide islands, and the enhanced surface area of the graphite substrate facilitating HO-H cleavage followed by H(ad) recombination, results in the high current density [200 mA/cm² at an overpotential of 0.3 V comparable to platinum (0.44 V)]. The easy method of fabrication of the electrode, which is also inexpensive, prompts us to explore its use in fabrication of solar-driven electrolysis.

General Strategy for the Synthesis of Transition-Metal Phosphide/N-Doped Carbon Frameworks for Hydrogen and Oxygen Evolution

Transition metal phosphides (TMPs) have been identified as promising nonprecious metal electrocatalyst for hydrogen evolution reaction (HER) and other energy conversion reactions. Herein, we reported a general strategy for synthesis of a series of TMPs (Fe₂P, FeP, Co₂P, CoP, Ni₂P, and Ni₁₂P₅) nanoparticles (NPs) with different metal phases embedded in a N-doped carbon (NC) matrix using metal salt, ammonium dihydrogen phosphate, and melamine as precursor with varying molar ratios and thermolysis temperatures. The resultant TMPs can serve as highly active and durable bifunctional electrocatalyst toward HER and oxygen evolution reaction (OER). In particular, the Ni₂P@NC phase only requires an overpotential of ∼138 mV to derive HER in 0.5 M H₂SO_4, and ∼320 mV for OER in 1.0 M KOH at the current density of 10 mA cm^-2. Because of the encapsulation of NC that can effectively prevent corrosion of embedded TMP NPs, Ni₂P@NC exhibits almost unfading catalytic performance even after 10 h under both acidic and alkaline solutions. This synthesis strategy provides a new avenue to exploring TMPs as highly active and stable electrocatalyst for the HER, OER, and other electrochemical applications.