Plum Pudding-Like Electrocatalyst of N-Doped SnOx@Sn Loaded on Carbon Matrix to Construct Photovoltaic CO2 Reduction System with Solar-to-Fuel Efficiency of 11.3%

A plum pudding-like Sn-based electrocatalyst is synthesized by calcinating the precursor SnC 2 O 4 on carbon black (CB) with polymeric carbon nitride (CN). This material exhibits a structure of a Sn metallic ball coated with a nitrogen-doped SnO x native layer (N-doped SnO x @Sn) embedded on a carbon matrix. The carbon matrix originates from the CB and the polymeric CN decomposition promotes electrical conductivity, leading to high electrochemical activity of the CN–Sn catalyst. The introduction of nitrogen that occupies the interstitial space of the surface SnO x layer further enhances electron transport; furthermore, it provides an electron-rich environment for oxygen because of its lower electronegativity, which is the fundamental cause of selectivity in the electrochemical reduction of CO 2 to CO. The maximum CO Faradaic efficiency over the optimal catalyst reaches 57.5%, with a high CO partial current density of 6.09 mA cm −2 at −0.7 V versus reversible hydrogen electrode. This catalyst is further applied to construct a photovoltaic–electrocatalytic CO 2 reduction/oxygen evolution reaction device to stably convert CO 2 to chemicals over 6 h at a high solar-to-fuel efficiency of 11.3%. This work explores a strategy of rational modulation on surface electronic structure to obtain high-performance electrocatalysts, inspiring the selectivity tuning in electrochemical CO 2 reduction via electronegativity difference of various elements.