Hexaminobenzene in conductive metal-organic frameworks as bifunctional electrocatalysts for overall water splitting and metal-air batteries

Developing highly efficient oxygen electrocatalysts is crucial in solving environmental and energy challenges. Herein, we leverage the design flexibility of 2D conductive metal-organic frameworks (c-MOFs) to conduct a comprehensive investigation of the activity of transition metal-hexaminobenzene (TM-HAB) for oxygen evolution reaction/oxygen reduction reaction/hydrogen evolution reaction (OER/ORR/HER) based on density functional theory (DFT) calculations. TM-HABs show sufficient structural stability and feasible synthesis according to the formation energy and dissolution potential criteria. Remarkably, Co-HAB exhibits low overpotentials of 0.32 and 0.48 V for OER and ORR, while Rh-HAB displays low overpotentials of 0.02 and 0.38 V for HER and OER, suggesting that they hold great potential as bifunctional catalysts for rechargeable metal-air batteries and water splitting, respectively. Additional volcano and contour plots reveal activity trends. The origin of activity is investigated through the d-band center of TM and bonding analysis. Intrinsic descriptors requiring no DFT data are proposed for rapid prediction of catalytic activity. The role of oxide formation enthalpies for metal atoms in activity prediction is highlighted. Our study not only demonstrates the superior properties of conductive metal-organic frameworks as bifunctional electrocatalysts but also provides valuable insights for the design and discovery of efficient catalysts.