Elucidating the electronic structures of β-Ag2MoO4 and Ag2O nanocrystals via theoretical and experimental approaches towards electrochemical water splitting and CO2 reduction

In this paper, we demonstrate a combined theoretical and experimental study on the electronic structure, and the optical and electrochemical properties of beta-Ag2MoO4 and Ag2O. These crystals were synthesized using the hydrothermal method and were characterized using X-ray diffraction (XRD), Rietveld refinement, and TEM techniques. XRD and Rietveld results confirmed that beta-Ag2MoO4 has a spinel-type cubic structure. The optical properties were investigated by UV-Vis spectroscopy. DFT+U formalism, via on-site Coulomb corrections for the d orbital electrons of Ag and Mo atoms (U-d) and the 2p orbital electrons of O atoms (U-p) provided an improved band gap for beta-Ag2MoO4. Examination of the density of states revealed the energy states in the valence and conduction bands of the beta-Ag2MoO4 and Ag2O. The theoretical band structure indicated an indirect band gap of approximately 3.41 eV. Furthermore, CO2 electroreduction, and hydrogen and oxygen evolution reactions on the surface of beta-Ag2MoO4 and Ag2O were studied and a comparative investigation on molybdate-derived silver and oxide-derived silver was performed. The electrochemical results demonstrate that beta-Ag2MoO4 and Ag2O can be good electrocatalysts for water splitting and CO2 reduction. The CO2 electroreduction results also indicate that CO2 reduction intermediates adsorbed strongly on the surface of Ag2O, which increased the overpotential for the hydrogen evolution reaction on the surface of Ag2O by as much as 0.68 V against the value of 0.6 V for Ag2MoO4, at a current density of -1.0 mA cm(-2).

Automated summary

This study demonstrates a combined theoretical and experimental investigation into the electronic structure, optical properties, and electrochemical behavior of beta-Ag2MoO4 and Ag2O. The results suggest that beta-Ag2MoO4 and Ag2O can serve as effective electrocatalysts for water splitting and CO2 reduction.