Development of cost-effective counter electrode (CE) materials is a key issue for practical applications of photoelectrochemical solar energy conversion. Kesterite Cu2ZnSnS4 (CZTS) has been recognized as a potential CE material, but its electrocatalytic activity is still insufficient for the recovery of I−/I3− electrolyte in dye-sensitized solar cells (DSSCs). Herein, we attempt to enhance the electrocatalytic activity of kesterite CZTS through element substitution of Zn2+ by Co2+ and Ni2+ cations, considering their high catalytic activity, as well as their similar atomic radius and electron configuration with Zn2+. The Cu2CoSnS4 (CCTS) and Cu2NiSnS4 (CNTS) CEs exhibit smaller charge-transfer resistance and reasonable power conversion efficiency (PCE) (CCTS, 8.3%; CNTS, 8.2%), comparable to that of Pt (8.3%). In contrast, the CZTS-based DSSCs only generate a PCE of 7.9%. Density functional theory calculation indicate that the enhanced catalytic performance is associated to the adsorption and desorption energy of iodine atom on the Co2+ and Ni2+. In addition, the stability of CCTS and CNTS CEs toward electrolyte is also significantly improved as evidenced by X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy characterizations. These results thus suggest the effectiveness of the element substitution strategy for developing high-performance CE from the developed materials, particularly for multicomponent compounds.

High-efficiency electrocatalysts have been widely applied in various fields, especially in the counter electrode (CE) of dye-sensitized solar cells (DSSCs). Different from the usual methods for developing highperformance CE materials through searching new materials and designing new nanostructure, we utilized a rapid surface sulfurization treatment to activate the well-known Co 3 O 4 material by increasing the adsorption energy of iodine (I) atom in the electrolyte of DSSCs. The density functional theory (DFT) calculation indicated the adsorption energy of Co 3 O 4 (E ad I 0.347 eV) toward I atom was dramatically increased to 0.835 eV through just transforming Co 3 O 4 at surface into Co 3 S 4 . After a short activation time of 30 s, Co 3 O 4 CEs showed a superior catalytic performance toward iodide electrolyte comparable with traditional Pt CE, generating a power conversion efficiency of 8.6% in DSSCs. This method of adjusting adsorption energy via surface sulfurization is applicable in the activation of other metal oxides, and provides a convenient but efficient way to modify the simple abundant materials for their different electrocatalytic applications.