Experimental and Computational Insights into the Overall Water Splitting Reaction by the Fe-Co-Ni-P Electrocatalyst

Chromium-Doped NiBP Micro-Sphere Electrocatalysts for Green Hydrogen Production under Industrial Operational Conditions

Wide spread adaptation of green hydrogen can help to mitigate the serious climate issues, increasing global energy demands and the development of advanced electrocatalysts robust under industrial conditions is one of the key technological challenges. Herein, chromium-doped nickel-boride-phosphide (Cr/NiBP) micro sphere (MS) electrocatalyst is demonstrated via a two-step hydrothermal approach along with post-annealing. The Cr/NiBP MS demonstrates low hydrogen evolution reaction and oxygen evaluation reaction over potentials of 78 and 250 mV at 100 mA cm-2 in 1 m KOH, out performing most of the reported catalysts. The Cr/NiBP ǁ Cr/NiBP exhibits only 1.54 V at 100 mA cm-2 in 1 m KOH and surpasses the benchmark of RuO2 (+) ǁ Pt/C (-) up to 2000 mA cm-2, which sets it as one of the best bifunctional electrocatalysts. Impressively, it maintains stable performance for over 240 h at 1000 mA cm-2 in 6 m KOH at 60°C, demonstrating rapid response, anti-corrosion resistance, and robust structural integrity to meet the industrial operational conditions. Further, Cr/NiBP ǁ Pt/C exhibits a super-low cell-voltage of 2.25 V at 2000 mA cm-2. The small amount of Cr atoms incorporation can significantly enhance active sites and intrinsic properties, accelerating water dissociation and rapid intermediate formation.

Fine Tuning of Torus-Shaped Mo-Doped Ni2P Nanorings for Enhanced Seawater Electrolysis

Seawater, as one of nature's most plentiful resources, provides a virtually inexhaustible source for generating hydrogen via water electrolysis. Developing an efficient bifunctional electrocatalyst for direct seawater splitting is challenging but highly desirable. Herein, a donut-shaped Mo-doped Ni2P nanoring electrocatalyst is developed, which is promising for direct overall seawater splitting. The optimized Mo0.1Ni1.9P catalyst shows low overpotentials and Tafel slopes in addition to high turnover frequencies, mass activities, and exchange current densities. The Mo0.1Ni1.9P||Mo0.1Ni1.9P couple-based electrolyzer requires a cell voltage of only 1.45 V in 1.0 m KOH and 1.47 V in untreated alkaline real seawater electrolysis at 10 mA cm-2 current density. Industrially required current densities of 500 and 1000 mA cm-2 are achieved at record low voltages of 1.81 and 1.86 V, respectively, at 25 °C and 1.77 and 1.82 V, respectively, at 75 °C for overall alkaline seawater splitting. The catalyst exhibited long-term stability at 400 mA cm-2 during alkaline seawater electrolysis. The synergy between Mo ions with multiple oxidation states and Ni ions, and nanoring morphology play a crucial role in increasing active sites for enhanced seawater dissociation. This work highlights the potential of Mo-doped Ni2P nanorings as unique catalysts for seawater electrolysis.

Rational Construction of a 3D Self-Supported Electrode Based on ZIF-67 and Amorphous NiCoP for an Enhanced Oxygen Evolution Reaction

The development of efficient and Earth-abundant electrocatalysts for the oxygen evolution reaction (OER) is an urgent requirement in the field of electrochemical water splitting. The electrocatalytic performance of the OER can be greatly enhanced by the synergistic combination of zeolite imidazolate frameworks (ZIFs) and transition-metal phosphides, both of which individually exhibit promising capabilities in this regard. In this study, a novel amorphous NiCoP deposited on ZIF-67 sheets supported on Ni foam (labeled as NiCoP/ZIF-67/NF) as an OER electrocatalytic material was successfully synthesized using a simple, secure, and time-efficient two-step strategy. The experimental results demonstrate that NiCoP/ZIF-67/NF possesses a large active surface area with abundant active sites. Also, the synergistic effect and interaction between NiCoP and ZIF-67, as well as between Ni and Co within NiCoP, effectively enhance its electrochemical performance under alkaline conditions. Consequently, NiCoP/ZIF-67/NF exhibits outstanding catalytic activity for OER with an overpotential (η) of 175 mV at a current density of 10 mA cm-2 and a long-term stability over 40 h at 20 mA cm-2 in a 1.0 M KOH electrolyte. The corresponding analyses suggest that the real active sites responsible for the OER are identified as NiOOH and CoOOH species within the structure of NiCoP/ZIF-67/NF. Additionally, the catalytic function and stability of ZIF-67 toward the OER under alkaline conditions were also briefly discussed. This work provides a novel catalytic material for the OER along with a facile strategy to fabricate superior, efficient, and noble metal-free catalysts suitable for energy-related applications.

Constructing Chainmail-Structured CoP/C Nanospheres as Highly Active Anodic Electrocatalysts for Oxygen Evolution Reaction

Constructing highly active and noble metal-free electrocatalysts is significant for the anodic oxygen evolution reaction (OER). Herein, uniform carbon-coated CoP nanospheres (CoP/C) are developed by a direct impregnation coupling phosphorization approach. Importantly, CoP/C only takes a small overpotential of 230 mV at the current density of 10 mA cm-2 and displays a Tafel slope of 56.87 mV dec-1. Furthermore, the intrinsic activity of CoP/C is 21.44 times better than that of commercial RuO2 under an overpotential of 260 mV. In situ Raman spectroscopy studies revealed that a large number of generated Co-O and Co-OH species could facilitate the *OH adsorption, effectively accelerating the reaction kinetics. Meanwhile, the carbon shell with a large number of mesoporous pores acts as the chainmail of CoP, which could improve the active surface area of the catalyst and prevent the Co sites from oxidative dissolution. This work provides a facile and effective reference for the development of highly active and stable OER catalysts.