Heteroatom-Doped Nickel Oxide for Electrooxidation of Methanol

Abstract

The current study emphasizes understanding the impact of impurities on the electrocatalytic efficiency of nickel oxide (NiO) for the methanol oxidation reaction (MOR) in 1 M KOH. It was evident that NiO with p-block elements, like boron (B) and sulfur (S), showed remarkable MOR activity with a low onset potential and better kinetic profile. NiO having both B and S exhibited MOR at a very low onset potential of 1.38 V vs RHE and a reduced Tafel slope of 42 mV dec-1. However, NiO having either B or S as an impurity showed onset potentials of 1.41 and 1.33 V vs RHE with higher Tafel slope values of 106 and 133 mV dec-1, respectively. The significant MOR activity of NiO with a low content of S and a slightly higher content of B was attributed to the change in the electronic structure with the reformation of the Fermi levels as evident from the density of states (DOS) and projected density of states (PDOS) calculations. Doping with B and S lowered the Fermi level of NiO from 2.196 to 2.070 eV. The doped NiO material also showed high stability and durability in an alkaline medium and retained the electrochemical activity for up to 12 h. The overall MOR process was investigated through FTIR and Raman studies. From the spectroscopic analyses, it was confirmed that the MOR proceeded via the formation of intermediates such as formate and carbonate.