Nickel-Based Single-Atom Catalyst toward Triiodide Reduction Reaction in Hybrid Photovoltaics

It is very significant to obtain highly efficient, cost-effective, and durable electrocatalysts toward triiodide reduction reaction (TRR) in hybrid photovoltaics. In this study, a nickel-based single-atom catalyst (SAC) (Ni-SAC) was prepared by the facile carbonization of NiPc@ZIF-8 and explored as a highly efficient Pt-free catalyst for TRR. During the carbonization process, the Ni species were separated by coordinate nitrogen atoms and distributed homogeneously within the porous carbon matrix, with the formation of the atomically dispersed Ni-N-4 active sites, revealed by the X-ray absorption fine structure and high-angle annular dark-field scanning transmission electron microscopy. Compared to the reference porous nitrogen-doped carbon, Ni-SAC exhibited superior catalytic activity toward TRR. More importantly, Ni-SAC possessed better stability over the triiodide/iodide redox couple than the Pt counterpart during the stability test. The resultant solar cell presented an efficiency of 7.42%, comparable to that of the Pt-based device (7.69%). Additionally, the Kelvin probe force microscopy measurement revealed that the enhanced catalytic activity of Ni-SAC originated from the moderate energy level matching with the triiodide/iodide redox couple. The formation of Ni-N4 active sites within the carbon matrix promoted the electron transferring at the interfaces of the catalyst/electrolyte. All results demonstrated that the SAC could be one of the Pt-free catalysts toward efficient TRR in hybrid photovoltaics.