Proposal of spin crossover as a reversible switch of catalytic activity for the oxygen evolution reaction in two dimensional metal–organic frameworks

The development of oxygen evolution reaction (OER) catalysts with high activity and controllability is crucial for clean energy conversion and storage but remains a challenge. Here, based on first-principles calculations, we propose to utilize spin crossover (SCO) in two-dimensional (2D) metal-organic frameworks (MOFs) to achieve reversible control of OER catalytic activity. The theoretical design of a 2D square lattice MOF with Co as nodes and tetrakis-substituted cyanimino squaric acid (TCSA) as ligands, which transforms between the high spin (HS) and the low spin (LS) state by applying an external strain (∼2%), confirms our proposal. In particular, the HS-LS spin state transition of Co(TCSA) considerably regulates the adsorption strength of the key intermediate HO* in the OER process, resulting in a significant reduction of the overpotential from 0.62 V in the HS state to 0.32 V in the LS state, thus realizing a reversible switch for the activity of the OER. Moreover, the high activity of the LS state is confirmed by microkinetic and constant potential method simulations.