Abstract
Although metal sulfides are promising catalysts for the electrochemical carbon dioxide (CO(2)) reduction reaction, repulsion between the lone pair of oxygen electrons of CO(2) and the electronic clouds of surface sulfur atoms is considered to impede the reaction. Nitrogen introduction is one potential solution to this problem; however, the optimal ratio of sulfur to nitrogen has yet to be determined, and the enhanced reaction products that have been reported to date are limited to carbon monoxide (CO) and formic acid. In this work, copper sulfide (Cu(2)S) and copper nitride (Cu(3)N) composites with varying sulfur-to-nitrogen ratios are synthesized with the objective of enhancing the catalytic activity of the CO(2) reduction reaction to methane (CH(4)). 4.20 mol% sulfur-containing Cu(3)N exhibits a Faradaic efficiency for CH(4) production that is higher than that of all examined catalysts including bare Cu(3)N and Cu(2)S. The results of in situ Fourier-transform infrared spectroscopy suggests that increased electron donation from the catalyst to the *CO intermediate by the introduction of sulfur into Cu(3)N shifts the selectivity of the reaction pathway from CO to CH(4) production. Taken together, the present findings demonstrate that sulfide-nitride composite structures can function as effective CO(2) reduction electrocatalysts to generate a variety of valuable products.