Study on NiMoO4/BiVO4/WO3 Heterojunction Photoanode to Enhance Photoelectrochemical Water Splitting Performance

Abstract

Due to the overconsumption of fossil fuels and the massive population worldwide, enormous energy requirements have become a significant issue. Considering this issue, the spread use of renewable energy has emerged as a proper solution for the sustainability of energy generation. Photoelectrochemical water splitting, which converts solar energy into hydrogen in the form of chemical energy, has become an efficient way to satisfy the claims of modern society. Electron-hole pair recombination is the critical factor for the advancement of photochemical performance. Therefore, fabrication of type II heterojunction structure attracts much attention in the charge separation process with the suitable band structure formation to minimize the recombination mechanism. In this work, NiMoO4/BiVO4/WO3 triple-layer photoanode has been synthesized with the concept of double-heterojunction to get high-efficiency performance in photoelectrochemical water splitting applications. Even though there are several methods for the fabrication of oxide nanostructures, simple hydrothermal and spin coating methods, which are low-cost and environmentally friendly, were implemented. Regarding material characterization, morphology, elemental and crystal structure are investigated through field emission scanning electron microscope (FESEM), X-ray diffractometry (XRD) analysis, X-ray photoelectron spectroscopy (XPS), and Ultraviolet photoelectron spectroscopy (UPS) to confirm successful synthesis and type II formation of WO3, BiVO4, and NiMoO4 heterostructures. Ultraviolet-visible (UV-Vis) spectroscopy is also performed to characterize the obtained electrode's optical properties and energy bandgap. Consequently, the construction of NiMoO4/BiVO4/WO3 triple-layer photoanode exhibits a photocurrent density of (2.30 mAcm-2 in KBi without Na2SO3) and (3.17 mAcm-2 in KBi with Na2SO3) at 1.23V vs. RHE, demonstrating the remarkable high chemical durability with regards to the modification of NiMoO4 semiconductor onto BiVO4/WO3 heterojunction photoanode.