Photoelectrocatalytic CO ₂ Reduction to C ₂ Products via the Morphology Control of a Three-Dimensional In ₂ S ₃ /CdS Heterojunction

In 2025, escalating consumption of fossil fuels has driven the atmospheric CO 2 concentration to 430 ppm, which is the highest value in human history. Photoelectrocatalytic CO 2 reduction offers a viable strategy to mitigate CO 2 levels, while addressing the surging demand for fossil energy. Herein, an in situ synthesis strategy of a solvothermal method combining with successive ionic layer adsorption and reaction (SILAR) was developed to fabricate a 3D honeycomb-structured In 2 S 3 /CdS heterojunction on carbon paper mimicking plant cells for PEC CO 2 reduction. The carbon paper substrate exhibits an excellent photothermal effect, with its surface temperature reaching 65 °C. Photochemical and photoelectrochemical analyses indicate that the formation of the heterojunction can effectively enhance the utilization of photogenerated carriers. Thus, the optimal In 2 S 3 /CdS-4h catalyst reduces CO 2 to HCOOH, CH 3 COOH, and CH 3 CH 2 OH products under mild reaction conditions, with a carbon-based product formation rate of 28.75 μM h –1 cm –2 and an electron selectivity for C 2 products of 88.8%. Repeated experiments reveal a favorable reproducibility of In 2 S 3 /CdS-4h photoelectrodes with the RSD lower than 10%. Moreover, the In 2 S 3 /CdS-4h heterojunction exhibits improved stability, retaining 70.5% of its initial activity after five cycles (10 h), whereas CdS retains only 53.8%. Considering the underlying mechanism, optical simulations and chemical field simulations confirm the benefits of this honeycomb structure on light absorption and C 2 product selectivity, respectively. Operando IR spectra identified the key *OCHO and *OC–COH intermediates responsible for the formation of the C 1 and C 2 products, respectively. Finally, DFT calculations show that the In 2 S 3 /CdS interface specifically promotes C–C coupling (forming *OC–COH) compared with the individual components. This work presents a perspective for the rational design of catalysts via multieffect synergy, advancing efficient PEC CO 2 reduction to C 2 products.