Surface engineering of Au nanostructures for plasmon-enhanced electrochemical reduction of N2 and CO2 into urea in the visible-NIR region

Abstract

The photoelectrochemical reduction of CO2 and N2 (N2CO2RR) is a promising method of producing urea under ambient conditions since highly active and stable electrocatalysts are desired. Plasmonic metals have attracted considerable attention due to their enhanced electrochemical activity at visible and near-infrared wavelengths (NIR). Herein, the morphology of Au was tuned to spherical nanoparticles, nanorods, and nanosheets by utilizing a variety of structure-directing agents. Among them, Au nanosheets (Au NSs) can absorb a broad spectrum of NIR wavelengths, enabling electrochemical reduction of N2 into NH3, with high yield rates and higher Faradic efficiency (FE) than most of the N2RR results reported. In addition, a distal associative pathway for N2RR into NH3 has been established over Au NSs. Additionally, the Au NSs photocathode demonstrates high stability over a period of 10 consecutive runs. In addition, this work provides a guide to fabricating highly stable photocathodes that convert N2 and CO2 into urea. Au NSs photocathode achieves a maximum urea yield rate of 98.5 µgureamgcat-1h−1 and FE of 22.7% at −0.7 V vs. RHE. Results show that the N2 and CO2 is the primary factor for urea production, whereas reducing NO3– and HCO3– contributes significantly to the total urea yield rate. Density functional theory calculations (DFT) reveal that Au NSs play a crucial role in promoting N2 and CO2 adsorption, activation, and stimulating the coupling reaction between C-N to form urea by the distal mechanism. As a result, this work opens up the possibility of developing hybrid catalytic systems for simultaneously reducing nitrate-containing wastewater and CO2, thus producing urea-rich treated water for agricultural use and achieving carbon neutrality.