Quasi-1D Aligned Nanostructures for Solar-Driven Water Splitting Applications: Challenges, Promises, and Perspectives

Solar energy conversion is considered to be one of the promising alternatives to fossil fuels. The photoelectrochemical (PEC) water splitting into hydrogen and oxygen is a prominent approach to utilize solar energy to produce clean hydrogen energy. In PEC water splitting, semiconductors play a central role for absorbing the solar radiations in the UV-visible region and generating electron-hole pairs that contribute to water splitting. This review provides an extensive overview of the 1D aligned nanoarrays (1D-NAs) and their architectures as photoactive materials. 1D-NAs can be in the form of nanorods (NRs), nanowires (NWs), nanopencils, and nanotubes (NTs), etc. The initial part of the review is dedicated to the synthesis and characterizations of the 1D-NAs, which is followed by useful synthetic protocols explicitly employed for the synthesis of NAs morphologies and the mechanisms involved in PEC water splitting. The final section of the review provides examples of highly anticipated TiO₂, ZnO, BiVO₄-based, and other miscellaneous aligned NAs utilized for PEC water splitting. The PEC water splitting performance of aligned NAs is compared with other morphologies in terms of photocurrent densities. In this review, it is attempted to provide an account of state-of-the-art stable, novel, and low-cost aligned photoactive materials for PEC water splitting.