Deciphering the synergistic role of chemisorbed phosphate on FeOOH for high-efficiency overall water splitting

Abstract

Oxyanion adsorption engineering has recently emerged as a hotspot in electrocatalysis due to its pivotal role in enhancing water oxidation performance. However, achieving simultaneous optimization of both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) activities via a single-component catalytic strategy, particularly within the context of developing cost-effective transition metal-based catalysts, remains a significant challenge in sustainable technologies. Herein, we report a phosphate ion modulation strategy to boost the bifunctional activity of FeOOH/NIF electrodes through chemisorption of PO₄³⁻. This approach not only accelerates the catalytic kinetics but also stabilizes the reaction intermediates during the OER and HER processes. Simultaneously, the in situ Raman results revealed that FeOOH undergoes a phase transformation from a single phase to a mixed phase under continuously increasing voltage, thereby significantly enhancing the OER and HER performance of FeOOH/NIF. As expected, the chemisorption of PO₄³⁻ by FeOOH/NIF enables ultra-low overpotentials: 232 mV at 100 mA cm⁻² for the OER and −308 mV at −100 mA cm⁻² for the HER. Meanwhile, the catalyst maintains stable performance for over 240 h at 100 and −100 mA cm⁻². Density functional theory (DFT) calculations confirm that chemisorbed phosphate ions effectively reduce the energy barrier of the rate-determining step in both the OER and HER, thereby improving the stability and activity of FeOOH/NIF. This study provides both experimental validation and theoretical insights for designing efficient bifunctional electrocatalysts through phosphate adsorption engineering.