Phosphorus Vacancy-Induced Spin-State Inhomogeneity for Enhanced Bifunctional Oxygen and Urea Oxidation

Efficient and durable catalysts are important for the oxygen evolution reaction (OER) and urea oxidation reaction (UOR) to achieve sustainable hydrogen production. However, the differences in binding energies of different intermediates pose challenges for achieving bifunctional catalysts. Herein, we present an advanced nickel-iron phosphide catalyst enriched with phosphorus vacancies (V_p-NiFeP/NF), which demonstrates an ultra-high activity of 222 mV at 10 mA cm⁻² in OER and 1.41 V at 100 mA cm⁻² in UOR with long-term stability. In situ Raman spectroscopy confirms that phosphorus vacancies accelerate surface reconstruction from Ni₂P to NiOOH, while in situ ATR-SEIRAS reveals that oxyanion suppresses OH⁻ adsorption, thereby enhancing the selectivity of the urea oxidation reaction. Moreover, phosphorus vacancies facilitate the breaking of C–N bond in urea, thus accelerating its decomposition. Density Functional Theory (DFT) research confirmed that vacancies induce localized inhomogeneous spin states of asymmetric nickel sites and simultaneously tune the binding energies of key intermediates in different pathways, thereby improving the catalytic efficiency of OER and UOR. This research provides a new strategy for developing high-performance electrocatalysts for water splitting and urea oxidation.