Fig. 4: Mechanistic exploration of A-Fe2S1N5/SNC for the OER.

a Free energy of a series of coverage fraction surfaces sampled for the A-Fe2S1N5/SNC catalysts; b The corresponding free energy change of the OER at the Fe−2 site; c comparison of Gibbs free energy changes of the OER intermediates in A-Fe2S1N5/SNC and Fe2N6/NC at U = 0 V; d the proposed 4e- mechanism of the OER on A-Fe2S1N5/SNC.