Electron Shuttling of Ni–Phosphate–Co Bridging Enables the Bidirectional Valence Modulation for Superior and Ultralong Water Splitting for Sustainable Green Hydrogen Production

The high-energy barrier and sluggish kinetics hinder
the conversion
efficiency of electrocatalytic water splitting. These limitations
can be mitigated by modulating the valence states of active sites
in nonprecious metal catalysts. However, achieving the synchronous
but opposite valence regulation of different metals in multicomponent
electrocatalysts remains a formidable challenge, especially when using
one-pot synthesis methods. Here, we propose a phosphate anion modification
strategy to endow the self-supporting NiCo materials (NiCoP@NF) with
efficient water-splitting performance. The phosphate species, amply
incorporated via one-step electrodeposition, form Ni–phosphate–Co-bridging
motifs in which phosphate anions serve as efficient electron conducting
pathways, rapidly shutting electrons from Ni to Co. Experimental analysis
and theoretical calculations reveal that this electron shuttling effect
induces the electron delocalization and redistribution around Ni and
Co centers, simultaneously triggering the low valence state of Co
and the high oxidation state of Ni in the integrated NiCoP@NF catalyst.
The valence-modulated metal sites own the rapid hydrogen diffusion
speed and deprotonation rate, obviously diminishing the energy cost
for the phase transformation of Ni2+/3+ into high valent
Ni3+σ/3+ as active oxygen evolution reaction (OER)
phases, inducing the high-level nonconcerted proton electron transfer
process during OER. Finally, NiCoP@NF exhibits excellent bifunctional
electrocatalytic performance, with a low overpotential of 50.2 mV
for hydrogen evolution reaction (HER) and an overpotential of 240
mV for OER at 10 mA cm–2. It also demonstrates great
durability, maintaining an industrial current density of 1 A cm–2 for ultralong 10,127 h stability, showing competitive
performance compared to most reported catalysts. Our study not only
validates an effective valence regulation strategy in the mixed metal
materials for achieving superb bifunctionality but also provides new
insights into designing robust multinary transition metal electrocatalysts
via oxyanion-induced electron bridging, offering promising prospects
for industrial applications.