Phosphorus vacancies improve the hydrogen evolution of MoP electrocatalysts

Synergistic Optimization of WP/WS2 Electrocatalyst by P/S Dual Vacancies and Heterojunctions for Hydrogen Evolution and Zn-H2O Batteries

Vacancy engineering is widely used to boost the hydrogen evolution reaction (HER) performance. However, dual-vacancy systems are more complex than mono-vacancy structures and remain underexplored. Key challenges involve developing emerging dual-vacancy catalysts, understanding their synergistic effects, and expanding their applications. Here, P/S dual vacancies were fabricated and coupled to heterostructures to improve HER performance. The as-synthesized WP/WS2-H heterostructures rich in P/S dual vacancies exhibit overpotentials of 175 and 170 mV at a current density of 10 mA cm-2 within 1 M KOH and 0.5 M H2SO4, respectively. The ability of P/S dual vacancies to promote HER activity of WP/WS2-H heterostructures is obviously higher than those of P and S mono-vacancy in WP-H and WS2-H. The heterojunctions of WP/WS2-H optimize the charge distribution, enhance the charge transfer rate, and increase the number of electrochemically active sites, thereby improving HER activities. Moreover, the as-fabricated Zn-H2O battery with WP/WS2-H as the cathode presents a maximum power density of up to 6.3 mW cm-2 and a stable discharge capacity of 69 h. This research not only provides a vigorous strategy for fabricating new dual-vacancy catalyst systems but also illustrates a synergistic effect and expands their application.

Facile Synthesis of MoP and Its Composite Structure with Ru as an Efficient Electrocatalyst for Hydrogen Evolution Reaction in Both Acidic and Alkaline Conditions

Developing low-cost electrocatalysts for efficient hydrogen evolution in both acidic and alkaline conditions is crucial for water-electrolytic hydrogen applications. Herein, MoP was synthesized via a simple, low-cost, and green phosphorization route. More importantly, the Ru/MoP composite prepared using the as-synthesized MoP as a reactant, which exhibited excellent catalytic activity for the hydrogen evolution reaction. It showed lower overpotentials of 108 and 55 mV at 10 mA·cm-2 in acidic and alkaline solutions, respectively, which are superior to those of bare Ru and pristine MoP as well as comparable or even better than those of previously reported excellent Ru- or MoP-based catalysts. In addition, it also demonstrated small Tafel slopes of 52.6 mV dec-1 and 67.9 mV dec-1 in acidic and alkaline solutions, respectively, along with long-term stability. This work provides an effective and feasible route to design high-efficient MoP-based electrocatalysts for hydrogen evolution reaction.

Carbonized Wood Decorated with Ternary Heterogeneous MoS2-MoP-Mo2C Nanoparticles for pH-Universal Hydrogen Evolution

The assembly of diverse active materials significantly enhances the efficiency of the electrocatalytic hydrogen evolution reaction (HER). Herein, we prepare a three-phase composite structure electrocatalyst on carbonized wood, in which molybdenum carbide and molybdenum phosphide are attached to molybdenum sulfide nanosheets (MoS2-MoP-Mo2C@CW) through the hydrothermal method in combination with high-temperature calcination for a pH-universal HER. MoS2 possesses abundant unsaturated coordination edge active sites, thus facilitating the adsorption and desorption of the hydrogen intermediate (H*). The synergistic effect between MoS2, MoP featuring favorable electronic conductivity, and Mo2C holding strong adsorption of H* enhances the catalytic activity for the pH-universal HER. Moreover, the carbonized wood with a hierarchical porous structure and aligned microchannels accelerates mass transport during the HER. As a result, the molybdenum-based self-supported composite electrode exhibits outstanding HER performance with the low overpotentials of 46, 84, and 65 mV to achieve the current density of 10 mA cm-2 and the corresponding Tafel slopes of 57, 111 mV, and 63 mV dec-1 in alkaline, neutral, and acidic environments, respectively. MoS2-MoP-Mo2C@CW also shows a long-term durability of 200 h over a broad pH range at 10 mA cm-2. This work provides an effective strategy for the development of multiphase carbonized wood-based electrocatalysts for the pH-universal HER.

Alkaline Hydrogen Evolution Reaction Electrocatalysts for Anion Exchange Membrane Water Electrolyzers: Progress and Perspective

For the aim of achieving the carbon-free energy scenario, green hydrogen (H2) with non-CO2 emission and high energy density is regarded as a potential alternative to traditional fossil fuels. Over the last decades, significant breakthroughs have been realized on the alkaline hydrogen evolution reaction (HER), which is a fundamental advancement and efficient process to generate high-purity H2 in the laboratory. Based on this, the development of the practical industry-oriented anion exchange membrane water electrolyzer (AEMWE) is on the rise, showing competitiveness with the incumbent megawatt-scale H2 production technologies. Still, great challenges lie in exploring the electrocatalysts with remarkable activity and stability for alkaline HER, as well as bridging the gap of performance difference between the three-electrode cell and AEMWE devices. In this perspective, we systematically discuss the in-depth mechanisms for activating alkaline HER electrocatalysts, including electronic modification, defect construction, morphology control, synergistic function, field effect, etc. In addition, the current status of AEMWE is reviewed, and the underlying bottlenecks that impede the application of HER electrocatalysts in AEMWE are summarized. Finally, we share our thoughts regarding the future development directions of electrocatalysts toward both alkaline HER and AEMWE, in the hope of advancing the commercialization of water electrolysis technology for green H2 production.

Sparkling Synergy: Enhancing Hydrogen Evolution with a Mesoporous CoP/FeP Interface

The reaction kinetics is predominantly determined by the surface and interface engineering of electrocatalysts. Herein, we demonstrate the growth of cobalt monophosphide and iron monophosphide (CoP/FeP) with an effective solid interface. The surface of CoP/FeP is mesoporous, which is obtained by phosphidizing mesoporous CoFe2O4. The CoP/FeP electrode exhibits substantially superior hydrogen evolution reaction (HER) performance compared to CoP and FeP. The overpotentials (η) required to generate 10 mA cm-2 are determined to be around 98 mVRHE (CoP/FeP), 220 mVRHE (FeP), and 265 mVRHE (CoP) in an acidic electrolyte. The exchange current density and Tafel slopes suggest that CoP/FeP has better redox properties and kinetic abilities compared to FeP and CoP. Furthermore, the CoP/FeP electrode exhibits reduced electrochemical impedance and superior surface charge transport characteristics in comparison to both the CoP and FeP electrodes. In addition to having a greater number of catalytically active sites, the turnover frequency of CoP/FeP is approximately 2 and 5 times higher than that of FeP and CoP, respectively. The CoP/FeP electrode maintains a consistent current density of around 25 mA cm-2 for a continuous period of 24 h during the HER, attesting to the excellent durability of the CoP/FeP electrode. In addition, a relationship between differential hydrogen adsorption energy (ΔEH), the corresponding Gibbs free energy change (ΔGH), and the hydrogen coverage on distinct surfaces, namely, CoP, FeP, and CoP/FeP, is established. The calculation findings show that the CoP/FeP surface, which is predominantly exposed with CoP, exhibits the highest catalytic potential for the HER. The estimation of the specific HER activity of the electrodes, normalized to the electrochemically active surface area, corroborates the calculation findings.

Phosphorous Vacancy and Built-In Electric Field Effect of Co-Doped MoP@MXene Heterostructures to Tune Catalytic Activity for Efficient Overall Water Splitting

Developing cost-effective, durable bifunctional electrocatalysts is crucial but remains challenging due to slow hydrogen/oxygen evolution reaction (HER/OER) kinetics in water electrolysis. Herein, a combined engineering strategy of phosphorous vacancy (Vp) and spontaneous built-in electric field (BIEF) is proposed to design novel highly-conductive Co-doped MoP@MXene heterostructures with phosphorous vacancy (Vp-Co-MoP@MXene). Wherein, Co doping regulates the surface electronic structure and charge re-distribution of MoP, Vp induces more defects and active sites, while BIEF accelerates the interfacial charge transfer rate between Vp-Co-MoP and MXene. Therefore, the synergistic integration of Vp-Co-MoP/MXene efficiently decreases activation energy and kinetic barrier, thus promoting its intrinsically catalytic activity and structural stability. Consequently, the Vp-Co-MoP@MXene catalyst displays low overpotentials of 102.3/196.5 and 265.0/320.0 mV at 10/50 mA cm-2 for HER and OER, respectively. Notably, two-electrode electrolyzers with the Vp-Co-MoP@MXene bifunctional catalysts to achieve 10/50 mA cm-2, only need low-cell voltages of 1.57/1.64 V in alkaline media. Besides, experimental and theoretical results confirm that the hetero-structure effectively reduces hydrogen adsorption free energy and rate-determining-step energy barrier of OER intermediates, thereby greatly boosting its intrinsically catalytic activity. This work verifies an effective strategy to fabricate efficient non-precious bifunctional electro-catalysts for water splitting via combination engineering of phosphorous vacancy, cation doping, and BIEF.

Ru doping and interface engineering synergistically boost the electrocatalytic performance of a WP/WP2 nanosheet array for an efficient hydrogen evolution reaction

The surface electronic structure and morphology of catalysts have a crucial impact on the electrocatalytic hydrogen evolution reaction performance. This work reports on the fabrication of a Ru-doped WP/WP2 heterojunction nanosheet array electrode via a one-step phosphating treatment of a Ru-doped WO3 precursor. Benefitting from the large electrochemical active surface of nanosheet arrays, rich WP/WP2 heterojunction interface, and trace Ru atom doping, the catalyst has a fairly low overpotential of 58.0 mV at 10 mA cm-2 and a Tafel slope of 50.71 mV dec-1 in acid solution toward the electrocatalytic HER. Further, theoretical calculations unveil that Ru atom doping and interface effect synergistically optimized the electronic structure of the catalyst and hence weakened the adsorption capacity of the catalyst surface toward hydrogen (H), which lowered the Gibbs free energy (ΔGH*) and consequently effectively improved the HER performance. This work may open new avenues for developing advanced nanoarray electrodes with efficient electrochemical energy conversion.

Design and multilevel regulation of transition metal phosphides for efficient and industrial water electrolysis

Renewable energy electrolysis of water to produce hydrogen is an effective measure to break the energy dilemma. However, achieving activity and stability at a high current density is still a key problem in water electrolyzers. Transition metal phosphides (TMPs), with high activity and relative inexpensiveness, have become excellent candidates for the production of highly pure green hydrogen for industrial applications. In this mini-review, multilevel regulation strategies including nanoscale control, surface composition and interface structure design of high-performance TMPs for hydrogen evolution are systematically summarized. On this basis, in order to achieve large-scale hydrogen production in industry, the hydrogen evolution performance and stability of TMPs at a high current density are also discussed. Peculiarly, the practical application and requirements in proton exchange membrane (PEM) or anion exchange membrane (AEM) electrolyzers can guide the advanced design of regulatory strategies of TMPs for green hydrogen production from renewable energy. Finally, the challenges and prospects in the future development trend of TMPs for efficient and industrial water electrolysis are given.

Current Progress of Mo-Based Metal Organic Frameworks Derived Electrocatalysts for Hydrogen Evolution Reaction

As an important half-reaction for electrochemical water splitting, electrocatalytic hydrogen evolution reaction suffers from sluggish kinetics, and it is still urgent to search high efficiency non-platinum-based electrocatalysts. Mo-based catalysts such as Mo2 C, MoO2 , MoP, MoS2 , and MoNx have emerged as promising alternatives to Pt/C owing to their similar electronic structure with Pt and abundant reserve of Mo. On the other hand, due to the adjustable topology, porosity, and nanostructure of metal organic frameworks (MOFs), MOFs are extensively used as precursors to prepare nano-electrocatalysts. In this review, for the first time, the progress of Mo-MOFs-derived electrocatalysts for hydrogen evolution reaction is summarized. The preparation method, structures, and catalytic performance of the catalysts are illustrated based on the types of the derived electrocatalysts including Mo2 C, MoO2 , MoP, MoS2 , and MoNx . Especially, the commonly used strategies to improve catalytic performance such as heteroatoms doping, constructing heterogeneous structure, and composited with noble metal are discussed. Moreover, the opportunities and challenges in this area are proposed to guide the designment and development of Mo-based MOF derived electrocatalysts.

Ultrafast Microwave Synthesis of Ru-Doped MoP with Abundant P Vacancies as the Electrocatalyst for Hydrogen Generation in a Wide pH Range

Molybdenum phosphide (MoP) has received increasing attention for the hydrogen evolution reaction (HER) due to its Pt-like electronic structure and high electrical conductivity. In this work, a flake-like Ru-doped MoP with phosphorus vacancy (Ru-MoP-P_V) electrocatalyst is synthesized for the first time by a simple and rapid room-temperature microwave approach within 30 s. The created abundant phosphorus vacancies provide rich active sites and favor rapid electron transfer. The introduced Ru also enhances the catalytic activity of the synthesized electrocatalyst efficiently. Then, the designed Ru-MoP-P_V possesses low overpotentials for HER with 79, 100, and 161 mV in 1.0 M KOH, 0.5 M H₂SO₄, and 1.0 M phosphate-buffered saline to obtain 10 mA cm^-2. The Ru-MoP-P_V and NiFe-layered double hydroxide are used as the cathode and the anode, respectively, to drive water splitting and just need a low cell voltage of 1.6 V to achieve 10 mA cm^-2. This work provides a feasible way for the rapid production of metal phosphides for energy conversion and storage applications.

P and Se Binary Vacancies and Heterostructures Modulated MoP/MoSe2 Electrocatalysts for Improving Hydrogen Evolution and Coupling Electricity Generation

It is not enough to develop an ideal hydrogen evolution reaction (HER) electrocatalysts by single strategy. Here, the HER performances are significantly improved by the combined strategies of P and Se binary vacancies and heterostructure engineering, which is rarely explored and remain unclear. As a result, the overpotentials of MoP/MoSe₂ -H heterostructures rich in P and Se binary vacancies are 47 and 110 mV at 10 mA cm^-2 in 1 m KOH and 0.5 m H₂ SO₄ electrolytes, respectively. Especially, in 1 m KOH, the overpotential of MoP/MoSe₂ -H is very close to commercial Pt/C at the beginning and even better than Pt/C when current density is over 70 mA cm^-2 . The strong interactions between MoSe₂ and MoP facilitate electrons transfer from P to Se. Thus, MoP/MoSe₂ -H possesses more electrochemically active sites and faster charge transfer capability, which are all in favor of high HER activities. Additionally, Zn-H₂ O battery with MoP/MoSe₂ -H as cathode is fabricated for simultaneous generation of hydrogen and electricity, which displays the maximum power density of up to 28.1 mW cm^-2 and stable discharging performance for 125 h. Overall, this work validates a vigorous strategy and provides guidance for the development of efficient HER electrocatalysts.

Cathode materials for halide-based aqueous redox flow batteries: recent progress and future perspectives

As the population increases sharply around the globe, huge shortages are occurring in energy resources. Renewable resources are urgently required to be developed to satisfy human demands. Unlike the lithium-ion batteries with safety and cost issues, the redox flow battery (RFB) is economical, stable, and convenient for the development of large-scale stationary electrical energy storage applications. Especially, the aqueous redox flow battery (ARFB) further exhibits a promising potential in larger power grids owing to its unique structural features of storing energy by filling the tank with electrolytes. The ARFB is capable of modulating battery parameters by controlling the volume and concentration of the electro-active species (EAS). Further, halogens show excellent properties, such as low cost and appropriate potential as an EAS for ARFB, further showing an efficient, safe, and affordable energy storage system (ESS). Moreover, to attain the demands of strong activity, high sensitivity, convenience as well as practicality, further attention needs to be paid to material (electrode) design and adjustment. In this mini-review, novel electrode materials, including their potential internal mechanisms and effective regulatory means, are summarized and applied in the zinc-halogen, hydrogen-halogen, and polysulfide-halogen ARFB systems, promoting the development of valuable material systems and the innovation of the energy storage/conversion technologies.