Multidimensional Nanostructures for Solar Water Splitting: Synthesis, Properties, and Applications

Abstract

Metal-oxide nanostructures have attractive properties for various applications, including alternative energy conversion and generation. Photoelectrochemical (PEC) and photovoltaic (PV) cells produced from metal oxides have potential to aid in producing low-cost and environmentally benign energy. Exploiting the unique properties of metal oxides at the nanoscale has witnessed an impressive surge in recent years. Advancement in the colloidal synthesis of these nanomaterials is quickly pushing the technology in making marketable sustainable alternative energy (SAE) a reality. While scientific research commences for SAE, a growing body of evidence is confirming anthropogenic climate change and accelerating the global need to reduce CO 2 emissions [1]. Currently global energy production is dominated by fossil-fuel combustion. The subsequent release of CO 2 into the atmosphere is being theorized to cause harm to the fragile environmental balance of planet Earth. One telling piece of evidence is the drastic increase in CO 2 levels after the industrial revolution, as evidenced by ice-core samples that track the oscillatory trends of atmospheric CO 2 over the past 600 millennia [2]. Many forms of SAE exist and include wind, solar, hydro, hydrothermal, photocatalysis and photoelectrochemical (PEC) technologies. Utilization of PEC devices for water splitting and oxygen/hydrogen production is a segment of study that has received

Synthesis and characterization of Ce and Er doped ZrO2 nanoparticles as solar light driven photocatalysts

“…In the past 20 years, researchers have mainly focused on other low-cost and abundant metal oxides (i.e. BiVO 4 , WO 3 ) [8,9] able to absorb visible light; or on the modification of high band gap materials such as TiO 2 or ZnO, by means of doping with transition-metal or non-metal ions [10], ion implantation, dye sensitization [11], or through the formation of hybrid nanostructures [12,13]. All of these systems are part of the so-called second-generation photoactive materials [6].…”

Comparison of photocatalytic and transport properties of TiO2 and ZnO nanostructures for solar-driven water splitting

“…Nevertheless many questions concerning the molecular mechanisms of water reduction and oxidation and the charge transfer dependence on the electronic and structural properties have not been completely solved yet, and the ideal semiconducting photocatalyst has still to be identified. In particular, one-dimensional nanostructures such as nanorods, nanotubes and nanowires have emerged as very promising alternative to nanoparticle-based architectures: the cylindrical and/or tubular configuration is very convenient to increase the surface area without affecting the total geometric surface and the unidirectional electric channel should allow a better charge transport 11 . The H2 photocatalytic generation involves three main steps: (i) absorption of photons (with energy higher than the semiconductor band gap (Eg) and consequent generation of electron/hole (e -/h + ) pairs in the semiconductor, (ii) excited charge carriers separation and migration within the semiconductor, and (iii) surface reaction of the carriers with water molecules.…”