Stable acidic water oxidation by tunable electronic states in β-PbO2 anode electrocatalyst aided by incorporation of various anions and cations

Abstract

Developing stable and cost-effective electrodes is one of the main challenges of clean hydrogen fuel production. However, the investigation of non-precious materials for this application, from both experimental and theoretical aspects, has been limited in scope. In the present research, the lead dioxide (β-PbO2) electrode was prepared by an anodic electrodeposition method on Ti substrate to use as the anode in electrochemical water splitting cells, where the oxygen evolution half-reaction occurs. The substitution of F– anion and Fe3+ and Co2+ cations into the structure of lead dioxide, to improve the properties and performance of these anodes, was investigated through a combination of experimental studies and quantum mechanical (QM) calculations. The β-PbO2, β-PbO2-F, β-PbO2-Fe, and β-PbO2-Co electrodes were characterized by the XRD, SEM, EDS, and electrochemical analyses, including CV, LSV, CP, and EIS. Furthermore, the electrode structures were investigated in theoretical studies by the density functional theory (DFT) method. The Gibbs energy change of intermediates formation and electronic properties, including band structure, the density of states, and charge density difference, were calculated and studied. The results showed that the substitutional elements improved the PbO2 activity toward oxygen evolution reaction (OER) by reducing the intermediates' adsorption resistance from 84.2 in pure PbO2 to 11.7 Ω.cm2 in PbO2-Fe. Fe3+ substitution had the most effect on durability and increased the efficient lifetime of the anode about 4 times relative to pure PbO2. The electrochemically active surface area (ECSA) was also increased intensively by doping Fe3+. It is concluded from the DFT calculations that the reaction energy barriers are reduced by ion incorporation. The OER overpotential decreases significantly from 920 mV on pure PbO2 surface to 350 mV by Co2+ substitution. The enhancement of the intrinsic activity of cation-substituted anodes was evidenced by the remarkable reduction of band gap energy at the Fermi level.