Tailoring CO2 Reduction with Doped Silicon Nanocrystals

More than 20 gigatonnes of carbon dioxide are released into the atmosphere every year. The conversion of CO2 into value-added chemicals and fuels by solar energy is an immediate solution to mitigate CO2 emissions, while providing global energy security. In this work, boron- and phosphorus-doped silicon nanocrystals (ncSi), comprised of three earth-abundant elements, are investigated for gas-phase heterogeneous photoreduction of CO2 for the first time. Surface dopants are demonstrated to induce CO2 adsorption capacity. Remarkably, phosphorus-doped ncSi is found to be the best performer among the singly doped and co-doped ncSi samples, doubling the rate of pristine ncSi. The enhancement of activity is attributed to the combination of the number of surface hydrides, its surface hydrophobicity, the addition of electronegative surface atoms, and perhaps an enhanced hydridic character of the SiH induced by the n-doping effect. Significantly, boron and phosphorus dopants are shown to provide increased stability of CO2 reduction activity compared to pristine ncSi after storing the samples in air for 2 weeks. These noteworthy findings open up a pathway to develop sustainable alternatives for existing photocatalysts for CO2 conversion.