Phytic Acid-Induced Oxygen Vacancies in Self-Supporting NiCo Metal-Organic Frameworks for Efficient Oxygen Evolution...

The sluggish kinetics of the oxygen evolution reaction (OER) impede efficient water electrolysis, motivating the development of robust, non-precious-metal electrocatalysts. Here, we construct a self-supported bimetallic metal-organic framework precatalyst (PAx-NiCo-BDC) through a two-step strategy using phytic acid (PA) for mild etching and multidentate coordination. This treatment introduces oxygen-vacancy-related coordination defects and regulates the precursor morphology. The optimized PA3-NiCo-BDC requires only 212 mV to reach 10 mA cm^{- 2}, exhibits a Tafel slope of 20.2 mV dec^{- 1}, and shows excellent durability, outperforming commercial RuO₂. An anion-exchange-membrane water electrolyzer employing PA3-NiCo-BDC delivers 1 A cm^{- 2} at 1.72 V and operates stably for 300 h. In situ Raman spectroscopy reveals that PA-induced defects enable the lower-potential formation of Ni³⁺-O-containing NiOOH-like surface species. Differential electrochemical mass spectrometry identifies the adsorbate evolution mechanism as the dominant OER pathway. Density functional theory calculations further show that defect-induced d-band-center modulation optimizes the adsorption and desorption of OER intermediates at Ni sites and lowers the OER energy barrier. This green coordination-engineering strategy provides a versatile route to efficient and durable MOF-based electrodes for practical water electrolysis.