The preparation of ionic liquid based iron phosphate/CNTs composite via microwave radiation for hydrogen evolution reaction and oxygen evolution reaction

Water electrolysis is a promising method for hydrogen production, so the preparation of low-cost and efficient electrocatalysts with a quick and simple procedure is crucial. Herein, iron phosphate (Fe₇(PO₄)₆) was prepared via microwave radiation using ionic liquid (IL) as iron and phosphorus dual-source. This method is simple and rapid, and the product can be directly used as electrocatalysts without further treatment. The experimental results show that the IL can influence the morphology and electrocatalytic performance. Moreover, the addition of carbon nanotubes (CNTs) is favorable for formation of iron phosphate nanoparticles to improve the catalytic activities. As hydrogen evolution reaction (HER) catalyst, this iron phosphate/CNTs exhibits an onset overpotential of 120 mV, Tafel slope of 32.9 mV dec^-1, and current densities of 10 mA cm⁻² at overpotential of 185 mV. Then, it obtains a good activity for oxygen evolution reaction (OER) with a low onset potential of 1.48 V, Tafel slope of 73.3 mV dec^-1, and it only needs an overpotential of 300 mV to drive the 10 mA cm⁻². This bifunctional catalyst also shows good durability for HER and OER. This microwave-assisted method provides an outstanding strategy to prepare iron phosphate in a simple and fast process with good catalytic performance for water splitting.     

In Situ Growth of Ultrafine Pt Nanoparticles onto Hierarchical Co3O4 Nanosheet-Assembled Microflowers for Efficient Electrocatalytic Hydrogen Evolution

The development of Pt-based electrocatalysts with high Pt utilization efficiency toward the hydrogen evolution reaction (HER) is of great significance for the future sustainable hydrogen economy. For rational design of high-performance HER electrocatalyst, the simultaneous consideration of both thermodynamic and kinetic aspects remains greatly challenging. Herein, a simple template-derived strategy is demonstrated for the in situ growth of ultrafine Pt nanoparticles onto Co₃O₄ nanosheet-assembled microflowers (abbreviated as Pt/Co₃O₄ microflowers hereafter) by using the pre-fabricated PtCo-based Hofmann coordination polymer as reactive templates. The elaborate preparation of such intriguing hierarchical architecture with well-dispersed tiny Pt nanoparticles, abundant metal/oxide heterointerfaces and open configuration endows the formed Pt/Co₃O₄ microflowers with high Pt utilization efficiency, rich active sites, lowered energy barrier for water dissociation and expedited reaction kinetics. Consequently, the Pt/Co₃O₄ microflowers exhibit superior HER activity with a relatively low overpotential of 34 mV to deliver a current density of 10 mA cm⁻², small Tafel slope (34 mV dec⁻¹) and outstanding electrochemical stability, representing an attractive electrocatalyst for practical water splitting. What's more, our concept of in situ construction of metal/oxide heterointerfaces may provide a new opportunity to design high-performance electrocatalysts for a variety of applications.     

Controlled Synthesis of 3D Flower‐like Ni2P Composed of Mesoporous Nanoplates for Overall Water Splitting

Developing efficient non‐noble metal and earth‐abundant electrocatalysts with tunable microstructures for overall water splitting is critical to promote clean energy technologies for a hydrogen economy. Herein, novel three‐dimensional (3D) flower‐like Ni₂P composed of mesoporous nanoplates with controllable morphology and high surface area was prepared by a hydrothermal method and low‐temperature phosphidation as efficient electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Compared with the urchin‐like Ni_x P_y , the 3D flower‐like Ni₂P with a diameter of 5 μm presented an efficient and stable catalytic performance in 0.5 m H₂SO₄, with a small Tafel slope of 79 mV dec⁻¹ and an overpotential of about 240 mV at a current density of 10 mA cm⁻² with a mass loading density of 0.283 mg cm⁻². In addition, the catalyst also exhibited a remarkable performance for the OER in 1.0 m KOH electrolyte, with an overpotential of 320 mV to reach a current density of 10 mA cm⁻² and a small Tafel slope of 72 mV dec⁻¹. The excellent catalytic performance of the as‐prepared Ni₂P may be ascribed to its novel 3D morphology with unique mesoporous structure.     

Ni2P Interlayer and Mn Doping Synergistically Expedite the Hydrogen Evolution Reaction Kinetics of Co2P

Transition metal phosphide is regarded as one of the most promising candidates to replace noble-metal hydrogen evolution reaction (HER) electrocatalysts. Nevertheless, the controllable design and synthesis of transition metal phosphide electrocatalysts with efficient and stable electrochemical performance are still very challenging. Herein, a novel hierarchical HER electrocatalyst consisting of three-dimensional (3D) coral-like Mn-doped Co₂P@an intermediate layer of Ni₂P generated in situ by phosphorization on Ni foam (MnCoP/NiP/NF) is reported. Notably, both the incorporation of Mn and introduction of the Ni₂P interlayer promote Co atoms to carry more electrons, which is beneficial to reduce the force of the Co−H bond and optimize the adsorption energy of hydrogen intermediate (|ΔG_H*|), thereby making MnCoP/NiP/NF exhibit outstanding HER performance with onset overpotential and Tafel slope as low as 31.2 mV and 61 mV dec⁻¹, respectively, in 1 m KOH electrolyte.     

Fe‐Doped Ni3C Nanodots in N‐Doped Carbon Nanosheets for Efficient Hydrogen‐Evolution and Oxygen‐Evolution Electrocatalysis

Uniform Ni₃C nanodots dispersed in ultrathin N‐doped carbon nanosheets were successfully prepared by carburization of the two dimensional (2D) nickel cyanide coordination polymer precursors. The Ni₃C based nanosheets have lateral length of about 200 nm and thickness of 10 nm. When doped with Fe, the Ni₃C based nanosheets exhibited outstanding electrocatalytic properties for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). For example, 2 at % Fe (atomic percent) doped Ni₃C nanosheets depict a low overpotential (292 mV) and a small Tafel slope (41.3 mV dec⁻¹) for HER in KOH solution. An outstanding OER catalytic property is also achieved with a low overpotential of 275 mV and a small Tafel slope of 62 mV dec⁻¹ in KOH solution. Such nanodot‐incorporated 2D hybrid structures can serve as an efficient bifunctional electrocatalyst for overall water splitting.     

Facile one-step synthesis of Ru doped NiCoP nanoparticles as highly efficient electrocatalysts for oxygen evolution reaction

Transition metal phosphides (TMPs) as ever-evolving electrocatalytic materials have attracted increasing attention in water splitting reactions owing to their cost-effective, highly active and stable catalytic properties. This work presents a facile synthetic route to NiCoP nanoparticles with Ru dopants which function as highly efficient electrocatalysts for oxygen evolution reaction (OER) in alkaline media. The Ru dopants induced a high content of Ni and Co vacancies in NiCoP nanoparticles, and the more defective Ru doped NiCoP phase than undoped NiCoP ones led to a greater number of catalytically active sites and improved electrical conductivity after undergoing electrochemical activation. The Ru doped NiCoP catalyst exhibited high OER catalytic performance in alkaline media with a low overpotential of 281 mV at 10 mA cm⁻² and a Tafel slope of 42.7 mV dec⁻¹.     

Amorphous Co-P Film: an Efficient Electrocatalyst for Hydrogen Evolution Reaction in Alkaline Seawater

Seawater electrolysis is considered an attractive alternative to conventional freshwater electrolysis for hydrogen production due to the abundance of seawater in nature. For this reason, efficient electrocatalysts for hydrogen evolution reaction (HER) in alkaline seawater are highly desired. In this study, we report an amorphous Co−P alloy on nickel foam (Co−P/NF) that behaves as an efficient and stable HER electrocatalyst for alkaline seawater electrolysis. The Co−P/NF presents high catalytic performance for HER, requiring a low overpotential of 213 mV to drive a current density of 100 mA cm⁻² and a Tafel slope of 120.2 mV dec⁻¹ in alkaline seawater. Furthermore, it shows remarkable electrochemical and structural stability in alkaline seawater.     

Heterostructured Inter-Doped Ruthenium–Cobalt Oxide Hollow Nanosheet Arrays for Highly Efficient Overall Water Splitting

The development of transition-metal-oxides (TMOs)-based bifunctional catalysts toward efficient overall water splitting through delicate control of composition and structure is a challenging task. Herein, the rational design and controllable fabrication of unique heterostructured inter-doped ruthenium–cobalt oxide [(Ru–Co)O_x] hollow nanosheet arrays on carbon cloth is reported. Benefiting from the desirable compositional and structural advantages of more exposed active sites, optimized electronic structure, and interfacial synergy effect, the (Ru–Co)O_x nanoarrays exhibited outstanding performance as a bifunctional catalyst. Particularly, the catalyst showed a remarkable hydrogen evolution reaction (HER) activity with an overpotential of 44.1 mV at 10 mA cm⁻² and a small Tafel slope of 23.5 mV dec⁻¹, as well as an excellent oxygen evolution reaction (OER) activity with an overpotential of 171.2 mV at 10 mA cm⁻². As a result, a very low cell voltage of 1.488 V was needed at 10 mA cm⁻² for alkaline overall water splitting.     

Molybdenum‐tungsten Oxide Nanowires Rich in Oxygen Vacancies as An Advanced Electrocatalyst for Hydrogen Evolution

Electrolysis of water is a promising way to produce hydrogen fuel in large scale. The commercialization of this technology requires highly efficient non‐noble metal electrocatalysts to decease the energy input for the hydrogen evolution reaction (HER). In this work, a novel nanowire structured molybdenum‐tungsten bimetallic oxide (CTAB‐D‐W₄MoO₃) is synthesized by a simple hydrothermal method followed with post annealing treatment. The obtained metal oxides feature with enhanced conductivity, rich oxygen vacancies and customized electronic structure. As such, the composite electrocatalyst exhibits excellent electrocatalytic performance for HER in an acidic environment, achieving a large current density of 100 mA cm^?2 at overpotential of only 286 mV and a small Tafel slope of 71.2 mV dec^?1. The excellent electrocatalytic HER performance of CTAB‐D‐W₄MoO₃ is attributed to the unique nanowire structure, rich catalytic active sites and promoted electron transfer rate.     

Carbon Nanotubes Decorated with CoP Nanocrystals: A Highly Active Non‐Noble‐Metal Nanohybrid Electrocatalyst for Hydrogen Evolution

The development of effective and inexpensive hydrogen evolution reaction (HER) electrocatalysts for future renewable energy systems is highly desired. The strongly acidic conditions in proton exchange membranes create a need for acid‐stable HER catalysts. A nanohybrid that consists of carbon nanotubes decorated with CoP nanocrystals (CoP/CNT) was prepared by the low‐temperature phosphidation of a Co₃O₄/CNT precursor. As a novel non‐noble‐metal HER catalyst operating in acidic electrolytes, the nanohybrid exhibits an onset overpotential of as low as 40 mV, a Tafel slope of 54 mV dec^?1, an exchange current density of 0.13 mA cm^?2, and a Faradaic efficiency of nearly 100 %. This catalyst maintains its catalytic activity for at least 18 hours and only requires overpotentials of 70 and 122 mV to attain current densities of 2 and 10 mA cm^?2, respectively.     

Facile and Large-Scale Fabrication of Sub-3 nm PtNi Nanoparticles Supported on Porous Carbon Sheet: A Bifunctional Material for the Hydrogen Evolution Reaction and Hydrogenation

Facile and large-scale preparation of materials with uniform distributions of ultrafine particles for catalysis is a challenging task, and it is even more difficult to obtain catalysts that excel in both the hydrogen evolution reaction (HER) and hydrogenation, which are the corresponding merging and splitting procedures of hydrogen, respectively. Herein, the fabrication of ultrafine bimetallic PtNi nanoparticles embedded in carbon nanosheets (CNS) by means of in situ self-polymerization and annealing is reported. This bifunctional catalyst shows excellent performance in the hydrogen evolution reaction (HER) and the hydrogenation of p-nitrophenol. Remarkably PtNi bimetallic catalyst with low metal loading (PtNi₂@CNS-600, 0.074 wt % Pt) exhibited outstanding HER activity with an overpotential as low as 68 mV at a current density of 10 mA cm⁻² with a platinum loading of only 0.612 μg_Pt cm⁻² and Tafel slope of 35.27 mV dec⁻¹ in a 0.5 m aqueous solution of H₂SO₄, which is comparable to that of the 20 % Pt/C catalyst (31 mV dec⁻¹). Moreover, it also shows superior long-term electrochemical durability for at least 30 h with negligible degradation compared with 20 % Pt/C. In addition, the material with increased loading (mPtNi₂@CNS-600, 2.88 % Pt) showed robust catalytic activity for hydrogenation of p-nitrophenol at ambient pressure and temperature. The catalytic activity towards hydrogen splitting is a circumstantial evidence that agrees with the Volmer–Tafel reaction path in the HER.     

Enhancing Hydrogen Evolution by Optimizing the Hydrogen Adsorption on Titanium Monoxide Nanodot-Decorated Cobalt Sulfide Nanosheets

Modulating the local electronic state of metal compounds through interfacial interaction has become a key method for manufacturing high-performance hydrogen evolution reaction (HER) electrocatalysts. The electron-rich active sites can promote the adsorption of hydrogen, which accelerates the Volmer step and thereby enhances the electrocatalytic performance of HER. Here, we found that the strong interfacial interaction between TiO nanodots (TiO/Co−S) and Co−S nanosheets could advantageously improve the performance toward HER of electrocatalyst. Meanwhile, XPS results showed that modulating the local electronic structure of the TiO nanodots produces electron-rich regions on Co. As a result, the overpotential of the TiO/Co−S nanocomposite at 10 mA cm⁻² was 107 mV, and the Tafel slope was 83.3 mV dec⁻¹. This study focused on the effect of the solid-solid interface on the local electronic structure of the catalytic metal active sites and successfully improved the catalytic activity of transition metal materials in HER catalysis.     

Platinum Oxide Nanoparticles for Electrochemical Hydrogen Evolution: Influence of Platinum Valence State

Electrochemical hydrogen generation is a rising prospect for future renewable energy storage and conversion. Platinum remains a leading choice of catalyst, but because of its high cost and low natural abundance, it is critical to optimize its use. In the present study, platinum oxide nanoparticles of approximately 2 nm in diameter are deposited on carbon nitride (C3N4) nanosheets by thermal refluxing of C3N4 and PtCl₂ or PtCl₄ in water. These nanoparticles exhibit apparent electrocatalytic activity toward the hydrogen evolution reaction (HER) in acid. Interestingly, the HER activity increases with increasing Pt⁴⁺ concentration in the nanoparticles, and the optimized catalyst even outperforms commercial Pt/C, exhibiting an overpotential of only −7.7 mV to reach the current density of 10 mA cm⁻² and a Tafel slope of −26.3 mV dec⁻¹. The results from this study suggest that the future design of platinum oxide catalysts should strive to maximize the Pt⁴⁺ sites and minimize the formation of the less active Pt²⁺ species.     

Self‐Supported Cu3P Nanowire Arrays as an Integrated High‐Performance Three‐Dimensional Cathode for Generating Hydrogen from Water

Searching for inexpensive hydrogen evolution reaction (HER) electrocatalysts with high activity has attracted considerable research interest in the past years. Reported herein is the topotactic fabrication of self‐supported Cu₃P nanowire arrays on commercial porous copper foam (Cu₃P NW/CF) from its Cu(OH)₂ NW/CF precursor by a low‐temperature phosphidation reaction. Remarkably, as an integrated three‐dimensional hydrogen‐evolving cathode operating in acidic electrolytes, Cu₃P NW/CF maintains its activity for at least 25 hours and exhibits an onset overpotential of 62 mV, a Tafel slope of 67 mV dec^?1, and a Faradaic efficiency close to 100 %. Catalytic current density can approach 10 mA cm^?2 at an overpotential of 143 mV.     

Hierarchical Tubular Architecture Constructed by Vertically Aligned CoS2-MoS2 Nanosheets for Hydrogen Evolution Electrocatalysis

Developing efficient electrocatalysts for the hydrogen evolution reaction (HER) is crucial for establishing a sustainable and environmentally friendly energy system, but it is still a challenging issue. Herein, hierarchical tubular-structured CoS₂-MoS₂/C as efficient electrocatalysts are fabricated through a unique metal–organic framework (MOF) mediated self-sacrificial templating. Core–shell structured MoO₃@ZIF-67 nanorods are used both as a precursor and a sacrificial template to form the one-dimensional tubular heterostructure where vertically aligned two-dimensional CoS₂-MoS₂ nanosheets are formed on the MOF-derived carbon tube. Trace amounts of noble metals (Pd, Rh, and Ru) are successfully introduced to enhance the electrocatalytic property of the CoS₂-MoS₂/C nanocomposites. The as-synthesized hierarchical tubular heterostructures exhibit excellent HER catalytic performance owing to the merits of the hierarchical hollow architecture with abundantly exposed edges and the uniformly dispersed active sites. Impressively, the optimal Pd-CoS₂-MoS₂/C-600 catalyst delivers a current density of 10 mA cm⁻² at a low overpotential of 144 mV and a small Tafel slope of 59.9 mV/dec in 0.5 m H₂SO₄. Overall, this MOF-mediated strategy can be extended to the rational design and synthesis of other hollow heterogeneous catalysts for scalable hydrogen generation.     

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.     

Hollow Iron–Vanadium Composite Spheres: A Highly Efficient Iron‐Based Water Oxidation Electrocatalyst without the Need for Nickel or Cobalt

Noble‐metal‐free bimetal‐based electrocatalysts have shown high efficiency for water oxidation. Ni and/or Co in these electrocatalysts are essential to provide a conductive, high‐surface area and a chemically stable host. However, the necessity of Ni or Co limits the scope of low‐cost electrocatalysts. Herein, we report a hierarchical hollow FeV composite, which is Ni‐ and Co‐free and highly efficient for electrocatalytic water oxidation with low overpotential 390 mV (10 mA cm⁻² catalytic current density), low Tafel slope of 36.7 mV dec⁻¹, and a considerable durability. This work provides a novel and efficient catalyst, and greatly expands the scope of low‐cost Fe‐based electrocatalysts for water splitting without need of Ni or Co.     

Ultrathin,Porous and Oxygen Vacancies‐Enriched Ag/WO3−x Heterostructures for Electrocatalytic Hydrogen Evolution

Exploring advanced electrocatalysts for electrocatalytic hydrogen evolution is highly desired but remains a challenge due to the lack of an efficient preparation method and reasonable structural design. Herein, we deliberately designed novel Ag/WO_3?x heterostructures through a supercritical CO₂‐assisted exfoliation‐oxidation route and the subsequent loading of Ag nanoparticles. The ultrathin and oxygen vacancies‐enriched WO_3?x nanosheets are ideal substrates for loading Ag nanoparticles, which can largely increase the active site density and improve electron transport. Besides, the resultant WO_3?x nanosheets with porous structure can form during the electrochemical cycling process induced by an electric field. As a result, the exquisite Ag/WO_3?x heterostructures show an enhanced hydrogen evolution reaction (HER) activity with a low onset overpotential of ≈30 mV, a small Tafel slope of ≈40 mV dec^?1 at 10 mA cm^?2, and as well as long‐term durability. This work sheds light on material design and preparation, and even opens up an avenue for the development of high‐efficiency electrocatalysts.     

Iron–Cobalt Phosphomolybdate with High Electrocatalytic Activity for Oxygen Evolution Reaction

Iron–cobalt phosphomolybdate (FeCoPM₁₂) nanoparticles, which are highly efficient catalytic materials for the oxygen evolution reaction (OER), were fabricated through a coprecipitation route. Compared with iron–cobalt hydroxide and state‐of‐the‐art RuO₂ electrocatalysts, the as‐prepared FeCoPM₁₂ sample exhibited robust OER catalytic activity with a low overpotential of 258 mV at a current density of 10 mA cm⁻² and a small Tafel slope of 33 mV dec⁻¹. Moreover, the as‐synthesized sample presented preferable stability and after 10 h at 1.52 V the current density degraded by merely 8.3 %. This is ascribed to the high electrochemical stability and small porous structure of FeCoPM₁₂, which provide effective electron transmission and improve the catalytic performance for OER in alkaline media.     

Tuning the Intrinsic Activity and Electrochemical Surface Area of MoS2 via Tiny Zn Doping: Toward an Efficient Hydrogen Evolution Reaction (HER) Catalyst

Molybdenum sulfide (MoS₂) is considered as an alternative material for commercial platinum catalysts for electrocatalytic hydrogen evolution reaction (HER). Improving the apparent HER activity of MoS₂ to a level comparable to that of Pt is an essential premise for the commercial use of MoS₂. In this work, a Zn-doping strategy is proposed to enhance the HER performance of MoS₂. It is shown that tiny Zn doping into MoS₂ leads to the enhancement of the electrochemical surface area, increases in proportion of HER active 1T phase in the material and formation of catalytic sites of higher intrinsic activity. These benefits result in a high-performance HER electrocatalyst with a low overpotential of 190 mV(@10 mA cm⁻²) and a low Tafel slope of 58 mV dec⁻¹. The origin for the excellent electrochemical performance of the doped MoS₂ is rationalized with both experimental and theoretical investigations.