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

Abstract

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.

The Role of Lattice Defects on the Optical Properties of TiO2 Nanotube Arrays for Synergistic Water Splitting

“…The preparation of TiO 2 NTAs followed an anodization process. − First, we polished Ti foil with different abrasive papers and then cleaned it in an ultrasound bath using acetone, ethanol for 5 min, and deionized water for 10 min. The Ti foil was chemically etched in a 20 mL solution of HF and HNO 3 (HF/HNO 3 /H 2 O = 1:4:5 in volume) for 30 s and washed with water.…”

Shape‐Controlled First‐Row Transition Metal Vanadates for Electrochemical and Photoelectrochemical Water Splitting

“…The efficiency and selectivity of the catalyst material towards a specific product can be enhanced by controlling its shape and size. [59,60] Particularly the quasi-1D (nanofibres, NWs, NRs) and 2D (layered, sheets) morphologies are of great interest as they offer maximum interface exposure, surface area, and active sites with controlled facet energies to assemble the incoming adsorbing species over electrode surface for selective chemical activity and product selectivity. [60,61] Furthermore, the controlled shape and defined surface features of materials effectively minimize electron-hole recombination to augment the electrokinetics and efficacy of the process.…”

“…Adjusting the balance between the electrolytic dissociation of reactants and the supersaturation of the solutions can also direct shapecontrolled growth. [60,62] For instance, the low electrolytic dissociation of reactants and weak electrolytes promoted the 1D and 2D anisotropic growth. In contrast for the 3D morphology, the composition should be changed to a strong electrolyte solution.…”

“…This reaction requires an additional energy input (typically supplied by a power source), as it is non-spontaneous and requires a positive thermodynamic free energy change (ΔG°) of + 237 kJ mol À 1 . [60] Due to the commercial aspects of EC-WS, researchers are investigating new materials to overcome the thermodynamic barriers to produce cheaper hydrogen fuel. [64,77] Co-based materials, including oxides, hydroxides, and sulphides, are of particular interest because of their high activity and robust nature.…”

Ni Foam Supported TiO2 Nanorod Arrays with CdS Branches: Type II and Z‐Scheme Mechanisms Coexisted Monolithic Catalyst Film for Improved Photocatalytic H2 Production

“…Among the various morphologies and structures, in situ synthesized highly ordered and vertically aligned 1D TiO 2 nanoarrays on a desirable monolithic substrate has attracted particular attention, which may become a class of practical catalytic system in the future application. [13,14] It is because that: 1) the monolithic catalysts are more recoverable and durable compared with powder photocatalysts; 2) by in situ synthesis, the monolithic catalysts possesses better mechanical properties and homogeneity, as well as excellent surface structure stability and binding strength without any addictive binder and conductive agent; 3) 1D nanoarrays structures can provide significant advantages for facile charge transport along the longitudinal dimensions, [15,16] which also manifested superior photovoltaic and regulatable super-hydrophilic/hydrophobic properties. [17] Depending on the categories of the substrates, two classifies of monolithic 1D TiO 2 nanoarrays-based photocatalysts have been developed.…”