Engineering metal-organic framework nanosheets with electronically modulated in-plane heterojunctions for robust high-current-density water splitting

To simultaneously achieve low overpotentials and stable operation for water splitting at high current densities, bifunctional electrocatalysts must be designed based on interfacial engineering for the oxygen/hydrogen evolution reaction (OER/HER). Herein, we report a boronization tactic to ingeniously tailor metal-organic frameworks (MOFs) anchored on iron foam (IF). The boron atoms induce the structural reconstitution of the Fe-MOF nanosheets, including the surface roughness, oxygen vacancies, and in-plane heterojunctions between crystalline Fe-MOF and amorphous Fe—B. The in-plane heterojunctions modulate the d-band center of the Fe sites to reduce the energy barrier of the OER/HER. As expected, the optimized Fe—B/Fe-MOF/IF only needed 1.44 and 1.53 V at 10 mA cm−2 to drive the OER and overall water splitting, respectively. The water-splitting system served at 500 mA cm−2 for 100 h with negligible structure variation and performance degradation. This work sheds light on the engineering of heterostructure interfaces and promotes the rational design of advanced electrocatalysts.