Cerium guided site-selective crystal disorder engineering of MIL-88B(Ni) frameworks for electrocatalysis offering high-performance water oxidation

Engineering the degree of crystallinity is an attractive route to expose unsaturated coordinative metal nodes that act as active electrocatalytic sites in metal-organic frameworks (MOFs). Herein, we develop a novel strategy to induce site-selective disordering of the crystalline structure of MIL88B(Ni) frameworks via Ce-doping, resulting crystalline/amorphous heterostructures. X-ray diffraction and electron microscopy analyses reveal that Ce-rich spherical regions in the framework are amorphous while Ce-deficient flat sheets are crystalline. Comparatively, an optimally Ce-doped MIL-88B(Ni)/NF(nickel foam) anode exhibits significantly lower overpotentials (η) of 205, 290, 410 and 450 mV to drive the oxygen evolution reaction (OER) under current densities of 10, 100, 1000 and 2000 mAcm⁻², respectively with a superior kinetic of 46.09 mVdec⁻¹ and a larger turnover frequency (TOF@η = 330 mV) of 0.36 s⁻¹. DFT calculations support the experimentally observed Ce³⁺ ion doping effect in inducing site-selective crystal disorder on MIL-88B(Ni) framework structure, and hence on the OER electrocatalytic activity enhancement. In addition to the remarkably high OER performance, the optimized Ce-doped MIL-88B(Ni)/NF anode exhibits superbly enhanced electrochemical durability over 146 h against industrially relevant high biases of up to 1000 mAcm⁻² in 1.0 M KOH solution, thus demonstrating that Ce-doped MIL88B(Ni)/NF is a highly promising industrially relevant high-performance anode material for electrocatalyzing the OER.