Metal(n+)-Metal(delta+) pair sites steer C-C coupling for selective CO2 photoreduction to C-2 hydrocarbons

The major obstacle for selective CO2 photoreduction to C-2 hydrocarbons lies in the difficulty of C-C coupling, which is usually restrained by the repulsive dipole-dipole interaction between adjacent carbonaceous intermediates. Herein, we first construct semiconducting atomic layers featuring abundant Metal(n+)-Metal(delta+) pair sites (0 < delta < n), aiming to tailor asymmetric charge distribution on the carbonaceous intermediates and hence trigger their C-C coupling for selectively yielding C-2 hydrocarbons. As an example, we first fabricate Co-doped NiS2 atomic layers possessing abundant Ni2+-Ni delta+ (0 < delta < 2) pairs, where Co doping strategy can ensure higher amount of Ni2+-Ni delta+ pair sites. In-situ Fourier-transform infrared spectroscopy, quasi in-situ Raman spectroscopy and density-functional-theory calculations disclose the Ni2+-Ni delta+ pair sites endow the adjacent CO intermediates with distinct charge densities, thus decreasing their dipole-dipole repulsion and hence lowering the rate-limiting C-C coupling reaction barrier. As a result, in simulated flue gas (10% CO2 balance 90% N-2), the ethylene selectivity for Co-doped NiS2 atomic layers reaches up to 74.3% with an activity of 70 mu g.g(-1).h(-1), outperforming previously reported photocatalysts under similar operating conditions.