Metal^{n +}-Metal^{δ +} pair sites steer C–C coupling for selective CO₂ photoreduction to C₂ hydrocarbons

The major obstacle for selective CO₂ photoreduction to C₂ 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 Metalⁿ⁺-Metal^δ+ pair sites (0 < δ < n), aiming to tailor asymmetric charge distribution on the carbonaceous intermediates and hence trigger their C–C coupling for selectively yielding C₂ hydrocarbons. As an example, we first fabricate Co-doped NiS₂ atomic layers possessing abundant Ni²⁺-Ni^δ+ (0 < δ < 2) pairs, where Co doping strategy can ensure higher amount of Ni ²⁺-Ni^δ+ pair sites. In-situ Fourier-transform infrared spectroscopy, quasi in-situ Raman spectroscopy and density-functional-theory calculations disclose the Ni²⁺-Ni^δ+ 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% N₂), the ethylene selectivity for Co-doped NiS₂ atomic layers reaches up to 74.3% with an activity of 70 μg·g⁻¹·h⁻¹, outperforming previously reported photocatalysts under similar operating conditions.