Design Strategies of Transition-Metal Phosphate and Phosphonate Electrocatalysts for Energy-Related Reactions

The Role of Alkali Metal Ions in Cooperative Electrocatalysis by Bifunctional Co-Mn-Mixed Phosphates

Developing cost-effective, non-precious metal bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is crucial for advancing sustainable energy storage and conversion technologies, including zinc-air batteries, fuel cells, and water electrolyzers. This study presents a one-pot synthesis of cobalt-manganese mixed phosphates as effective bifunctional electrocatalysts for both ORR and OER. Among the catalysts tested, Na-Co-Mn-P [NaCo1.5Mn1.5(HPO4)2(PO4)] exhibited the highest catalytic activity, with a minimal ΔE of 0.86 V, indicating superior performance. The incorporation of alkali metals and the synergistic effects of metal and phosphate components enhance conductivity, electrochemical surface area, and mixed valency of transition metals, contributing to improved electrocatalytic activity. This work highlights a straightforward synthesis method and the beneficial role of metal-phosphate synergy in oxygen electrocatalysis.

Structural Regulation of a Multi-Component Co2P2O7-MoN/NC Electrocatalyst for Efficient Oxygen Evolution Reaction

Realizing efficient and durable non-precious metal-based electrocatalysts for oxygen evolution reaction (OER) still remains a great challenge. Here, a multi-component composite of Co2P2O7-MoN/NC containing pyrophosphate, nitride, and nitrogen-doped carbon is successfully prepared via a facile two-step synthesis method. Combining the structural regulation between the active metal- and non-metal-based species, Co2P2O7-MoN/NC demonstrates superior activity and durability for OER, requiring an overpotential of 278 mV at a current density of 10 mA cm-2, a Tafel slope of 83.3 mV dec-1, and long-term stability over 100 h in an alkaline solution. Post-characterizations reveal that synergistic effect among stable Co2P2O7, partially dissolved MoN, N-doped carbon, and new-formed CoOOH nanosheets enable structural reconstruction, fast charge transfer, and formation of oxygen-containing intermediates, promoting the OER performance significantly. This work provides a promising pathway to tune multi-components to fabricate efficient transition-metal-based electrocatalysts in energy conversion applications.

Porous Flower-Like Nanoarchitectures Derived from Nickel Phosphide Nanocrystals Anchored on Amorphous Vanadium Phosphate Nanosheet Nanohybrids for Superior Overall Water Splitting

Transition metal phosphides (TMPs) and phosphates (TM-Pis) nanostructures are promising functional materials for energy storage and conversion. Nonetheless, controllable synthesis of crystalline/amorphous heterogeneous TMPs/TM-Pis nanohybrids or related nanoarchitectures remains challenging, and their electrocatalytic applications toward overall water splitting (OWS) are not fully explored. Herein, the Ni2P nanocrystals anchored on amorphous V-Pi nanosheet based porous flower-like nanohybrid architectures that are self-supported on carbon cloth (CC) substrate (Ni2P/V-Pi/CC) are fabricated by conformal oxidation and phosphorization of pre-synthesized NiV-LDH/CC. Due to the unique microstructures and strong synergistic effects of crystalline Ni2P and amorphous V-Pi components, the obtained Ni2P/V-Pi/CC owns abundant active sites, suitable surface/interface electronic structure and optimized adsorption-desorption of reaction intermediates, resulting in outstanding electrocatalytic performances toward hydrogen and oxygen evolution reactions in alkaline media. Correspondingly, the assembled Ni2P/V-Pi/CC||Ni2P/V-Pi/CC electrolyzer only needs an ultralow cell voltage (1.44 V) to deliver 10 mA cm-2 water-splitting currents, exceeding its counterparts, recently reported bifunctional catalysts-based devices, and Pt/C/CC||IrO2/CC pairs. Moreover, the Ni2P/V-Pi/CC||Ni2P/V-Pi/CC manifests remarkable stability. Also, such device shows a certain prospect for OWS in acidic media. This work may spur the development of TMPs/TMPis-based nanohybrid architectures by combining structure and phase engineering, and push their applications in OWS or other clean energy options.

In Situ Reconstruction NiO Octahedral Active Sites for Promoting Electrocatalytic Oxygen Evolution of Nickel Phosphate

Electrochemical activation strategy is very effective to improve the intrinsic catalytic activity of metal phosphate toward the sluggish oxygen evolution reaction (OER) for water electrolysis. However, it is still challenging to operando trace the activated reconstruction and corresponding electrocatalytic dynamic mechanisms. Herein, a constant voltage activation strategy is adopted to in situ activate Ni₂ P₄ O₁₂ , in which the break of NiONi bond and dissolution of PO₄ ^3- groups could optimize the lattice oxygen, thus reconstructing an irreversible amorphous Ni(OH)₂ layer with a thickness of 1.5-3.5 nm on the surface of Ni₂ P₄ O₁₂ . The heterostructure electrocatalyst can afford an excellent OER activity in alkaline media with an overpotential of 216.5 mV at 27.0 mA cm^-2 . Operando X-ray absorption fine structure spectroscopy analysis and density functional theory simulations indicate that the heterostructure follows a nonconcerted proton-electron transfer mechanism for OER. This activation strategy demonstrates universality and can be used to the surface reconstruction of other metal phosphates.

The crystal structure of cobalt cadmium bis(hydrogenphosphate) bis(phosphate(V)) tetrahydrate, H10O20P4Co3.14Cd1.86

H10O20P4Co3.14Cd1.86, monoclinic, C2/c (no. 15), a = 17.5779(6) Å, b = 9.0747(3) Å, c = 9.4946(3) Å, β = 96.636(3)°, V = 1504.38(9) Å3, Z = 1, R gt (F) = 0.0273, wR ref (F 2) = 0.0646, T = 293(2) K.

Conductive One-Dimensional Coordination Polymers with Tunable Selectivity for the Oxygen Reduction Reaction

Conductive materials involving nonprecious metal coordination complexes as electrocatalysts for the oxygen reduction reaction (ORR) have received increasing attention in recent years. Herein, we reported efficient ORR electrocatalysts containing M-S2N2 sites with tunable selectivity based on simple one-dimensional (1D) coordination polymers (CPs). The 1D CPs were synthesized from M(OAc)2 and 2,5-diamino-1,4-benzenedithiol (DABDT) by a solvent thermal method. Due to their good electrical conductivities (10-6-10-2 S cm-1), the 1D CPs could be used as ORR catalysts in low catalytic amounts without the addition of carbon materials. Cobalt-based CPs showed a well-organized structure of nanosheets with Co-S2N2 sites exposed and exhibited remarkable electrocatalytic ORR activity (Eonset = 0.93 V vs reversible hydrogen electrode (RHE), E1/2 = 0.82 V, n = 3.85, JL = 5.22 mA cm-2, Tafel slope of 63 mV dec-1) in alkaline media. However, nickel-based CPs favored a 2e- ORR process with ∼87% H2O2 selectivity and an Eonset of 0.78 V. This work provides new opportunities for the construction of ORR catalysts based on conductive nonprecious metal CPs.

Activity Promotion of Core and Shell in Multifunctional Core-Shell Co2 P@NC Electrocatalyst by Secondary Metal Doping for Water Electrolysis and Zn-Air Batteries

Developing cost-efficient multifunctional electrocatalysts is highly critical for the integrated electrochemical energy-conversion systems such as water electrolysis based on hydrogen/oxygen evolution reactions (HER/OER) and metal-air batteries based on OER/oxygen reduction reactions (ORR). The core-shell structured materials with transition metal phosphide as the core and nitrogen-doped carbon (NC) as the shell have been known as promising HER electrocatalysts. However, their oxygen-related electrocatalytic activities still remain unsatisfactory, which severely limits their further applications. Herein an effective strategy to improve the core and shell performances of core-shell Co₂ P@NC electrocatalysts through secondary metal (e.g., Fe, Ni, Mo, Al, Mn) doping (termed M-Co₂ P@M-N-C) is reported. The as-synthesized M-Co₂ P@M-N-C electrocatalysts show multifunctional HER/OER/ORR activities and good integrated capabilities for overall water splitting and Zn-air batteries. Among the M-Co₂ P@M-N-C catalysts, Fe-Co₂ P@Fe-N-C electrocatalyst exhibits the best catalytic activities, which is closely related to the configuration of highly active species (Fe-doping Co₂ P core and Fe-N-C shell) and their subtle synergy, and a stable carbon shell for outstanding durability. Combination of electrochemical-based in situ Fourier transform infrared spectroscopy with extensive experimental investigation provides deep insights into the origin of the activity and the underlying electrocatalytic mechanisms at the molecular level.

Highly Dispersed Pt Nanoparticles Embedded in N-Doped Porous Carbon for Efficient Hydrogen Evolution

A novel and facile strategy is presented to synthesize highly dispersed Pt nanoparticles embedded in N-doped porous carbon (Pt@NPC) via carbonization of Zn-containing metal-organic frameworks and chemical replacement of Zn with Pt. The as-prepared Pt@NPC exhibits superior activity and durability towards hydrogen evolution reaction (HER) in comparison with commercial Pt/C catalyst. The excellent HER performance of Pt@NPC can be ascribed to the combined features of catalyst and support material, including high dispersion and ultrathin particle size of Pt, high surface area and nitrogen doping of carbon support, and the strong interaction between metal and support.

Aqueous Rechargeable Zn-N2 Battery Assembled by Bifunctional Cobalt Phosphate Nanocrystals-Loaded Carbon Nanosheets for Simultaneous NH3 Production and Power Generation

Developing cost-effective and controllable technologies beyond traditional overall N₂ electrocatalysis is critical for the large-scale production of NH₃ through electrochemical N₂ reduction reaction (NRR) under ambient conditions. Herein, the aqueous rechargeable Zn-N₂ battery, assembled by coupling the bifunctional cobalt phosphate nanocrystals-loaded heteroatoms-doped carbon nanosheets (CoPi/NPCS) as cathode electrocatalyst and the commercial Zn plate as anode with KOH electrolyte, was fabricated for the sustainable reduction of N₂ to NH₃ and power generation during discharge process. Benefiting from the desirable active components of cobalt phosphate nanocrystals and the synergistic effect between nanocrystals and carbon substrates, the CoPi/NPCS catalyst exhibits the enhanced NRR and oxygen evolution reaction (OER) performance in alkaline electrolyte. And the cobalt phosphates are confirmed as active components through the associative pathway toward NRR. When measured in the flow battery configuration with gas diffusion electrode by flowing N₂ during discharge, this CoPi/NPCS-catalyzed Zn-N₂ battery enables the high N₂-to-NH₃ yield rate of 14.7 μg h^-1 mg_cat.^-1 and Faradaic efficiency of 16.35% at 0.6 V vs Zn²⁺/Zn, which can be able to maintain stable in discharge processes during cycling tests. Moreover, the impressive power output of the peak power density of 0.49 mW cm^-2 and the energy density of 147.6 mWh g_zn^-1 are still achieved by this Zn-N₂ battery, which are both higher than those of previously reported Zn-N₂ batteries. This work not only provides the guideline for the rational design of robust and active bifunctional NRR-OER catalysts but also develops a reasonable and promising technology for efficient electrochemical N₂-to-NH₃ and power generation.

Boosting electrocatalytic oxygen evolution activity of bimetallic CoFe selenite by exposing specific crystal facets

It was of great significance to develop efficient and stable electrocatalysts for oxygen evolution reactions via simple and environmentally-friendly methods.