Tungstic acid integrated metal–organic frameworks for efficient oxygen evolution reaction

Abstract

Transition metal oxide-based catalysts are known as the most active oxygen evolution reaction (OER) catalysts due to their intrinsic electronic structures and binding strength of oxygenated intermediates. However, even the most active transition metal oxide-based OER catalysts have a turnover frequency far lower than that of the oxygen-evolving complexes in biological systems for intermolecular site aggregation. Herein, we implement the hybridization of a metal–organic framework and tungstic acid (WO₃·xH₂O-in-MIL-88) to achieve ordered FeNi site isolation at the molecular level and avoid intermolecular decomposition during the catalysis process. The optimized hybrid with 15% tungstic acid (15%-WO₃·xH₂O-in-MIL-88) achieves a much-enhanced OER activity and stability in terms of a low overpotential of 263 mV to reach a current density of 10 mA cm⁻², a low Tafel slope of 39 mV dec⁻¹, and long-term stability, which is much superior to that of the commercial RuO₂ catalyst.