Solar-driven water splitting provides a leading approach to store the abundant yet intermittent solar energy and produce hydrogen as a clean and sustainable energy carrier. A straightforward route to light-driven water splitting is to apply self-supported particulate photocatalysts, which is expected to allow solar hydrogen to be competitive with fossil-fuel-derived hydrogen on a levelized cost basis. More importantly, the powder-based systems can lend themselves to making functional panels on a large scale while retaining the intrinsic activity of the photocatalyst. However, all attempts to generate hydrogen via powder-based solar water-splitting systems to date have unfortunately fallen short of the efficiency values required for practical applications. Photocatalysis on photocatalyst particles involves three sequential steps: (i) absorption of photons with higher energies than the bandgap of the photocatalysts, leading to the excitation of electron–hole pairs in the particles, (ii) charge separation and migration of these photoexcited carriers, and (iii) surface chemical reactions based on these carriers. In this review, we focus on the challenges of each step and summarize material design strategies to overcome the obstacles and limitations. This review illustrates that it is possible to employ the fundamental principles underlying photosynthesis and the tools of chemical and materials science to design and prepare photocatalysts for overall water splitting.

We demonstrate a concept of potentially inexpensive sunlight-powered watersplitting reactors using a fixed Al-doped SrTiO 3 photocatalyst. A panel reactor filled with only a 1-mm-deep layer of water was capable of rapid release of product gas bubbles without forced convection. A flat panel reactor with 1 m 2 of lightaccepting area retained the intrinsic activity of the photocatalyst and achieved a solar-to-hydrogen energy conversion efficiency of 0.4% by water splitting under natural sunlight irradiation.

Development of sunlight-driven water splitting systems with high efficiency, scalability, and cost-competitiveness is a central issue for mass production of solar hydrogen as a renewable and storable energy carrier. Photocatalyst sheets comprising a particulate hydrogen evolution photocatalyst (HEP) and an oxygen evolution photocatalyst (OEP) embedded in a conductive thin film can realize efficient and scalable solar hydrogen production using Z-scheme water splitting. However, the use of expensive precious metal thin films that also promote reverse reactions is a major obstacle to developing a cost-effective process at ambient pressure. In this study, we present a standalone particulate photocatalyst sheet based on an earth-abundant, relatively inert, and conductive carbon film for efficient Z-scheme water splitting at ambient pressure. A SrTiO:La,Rh/C/BiVO:Mo sheet is shown to achieve unassisted pure-water (pH 6.8) splitting with a solar-to-hydrogen energy conversion efficiency (STH) of 1.2% at 331 K and 10 kPa, while retaining 80% of this efficiency at 91 kPa. The STH value of 1.0% is the highest among Z-scheme pure water splitting operating at ambient pressure. The working mechanism of the photocatalyst sheet is discussed on the basis of band diagram simulation. In addition, the photocatalyst sheet split pure water more efficiently than conventional powder suspension systems and photoelectrochemical parallel cells because H and OH concentration overpotentials and an IR drop between the HEP and OEP were effectively suppressed. The proposed carbon-based photocatalyst sheet, which can be used at ambient pressure, is an important alternative to (photo)electrochemical systems for practical solar hydrogen production.

The effects of preparation methods, calcination times, and La doping concentrations on the crystallinity, visible light absorption, and photocatalytic water splitting performance of Rh- and La-codoped SrTiO3 (SrTiO3:La/Rh) were investigated. Applying a two-step solid state reaction in which SrTiO3 acted as a perovskite-type host produced core/shell structured SrTiO3:La/Rh, the surface of which was enriched with the dopants. La doping suppressed the formation of oxygen vacancies and inactive Rh4+ species. Under visible light irradiation (λ > 420 nm), SrTiO3:La/Rh exhibited 3.5 and 3.8 times higher rates of H2 evolution in an aqueous methanol solution and during redox-free Z-scheme overall water splitting in combination with Ir/CoO x /Ta3N5, respectively, compared to SrTiO3:Rh. The solar-to-hydrogen efficiency of the Z-scheme system as measured under illumination with simulated sunlight (AM1.5G) was found to have improved by a factor of 3.

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Harvesting solar energy to convert CO 2 into chemical fuels is a promising technology to curtail the growing atmospheric CO 2 levels and alleviate the global dependence on fossil fuels. However, the assembly of efficient and robust systems for the selective photoconversion of CO 2 without sacrificial reagents and external bias remains a challenge. Here, we present a photocatalyst sheet that converts CO 2 and H 2 O into formate and O 2 as a potentially scalable technology for CO 2 utilisation. This technology integrates La and Rh-doped SrTiO 3 (SrTiO 3 :La,Rh) and Mo-doped BiVO 4 (BiVO 4 :Mo) light absorbers modified by phosphonated Co(II) bis(terpyridine) and RuO 2 catalysts onto a gold layer. The monolithic device provides a solar-to-formate conversion efficiency of 0.08±0.01% with a selectivity for formate of 97±3%. As the device operates wirelessly and uses water as an electron donor, it offers a versatile strategy toward scalable and sustainable CO 2 reduction using molecular-based hybrid photocatalysts.

Molybdenum trioxide (MoO3) has recently aroused intensive interest as a renowned conversion‐type anode of Li‐ion batteries (LIBs). Nevertheless, the inferior rate capability, sluggish reaction kinetics, and fast capacity decay during a long‐term charge/discharge process seriously inhibits large‐scale commercial application. Herein, abundant oxygen vacancies and MXene nanosheets are elaborately introduced into MoO3 nanobelts through hydrazine reduction and electrostatic assembly to accelerate the ionic and electronic diffusion/transport kinetics for LIBs. Benefitting from the accelerated ion diffusion kinetics, enhanced electrical conductivity, and additional active sites induced by oxygen vacancies as well as the robust interfacial contact, the prepared MoO3−x/MXene heterostructure exhibits excellent lithium‐ion storage performances. First‐principles calculations indicate that the adsorption of Li+ ion and the electrical conductivity are significantly enhanced for the MoO3−x/MXene heterostructure. Thus, the composite exhibits high reversible capacity of 1258 mAh g−1 at 0.1 A g−1 for Li‐ion storage and retains 474 mAh g−1 at 10 A g−1, remarkably higher than those of the previously reported MoO3‐based anode materials. More importantly, the composite is fabricated with commercial LiFePO4 into a full LIB, which displays an unparalleled energy density of 330 Wh kg−1.

Co-containing layered double hydroxides (LDHs) are potential non-noble-metal catalysts for the aerobic oxidation of alcohols. However, the intrinsic activity of bulk LDHs is relatively low. In this work, we fabricated ultrathin and vacancy-rich nanosheets by exfoliating bulk CoAl-LDHs, which were then assembled with graphite oxide (GO) to a ord a hybrid CoAl-ELDH/GO catalyst. TEM, AFM, and positron annihilation spectrometry indicate that the thickness of the exfoliated LDH platelets is about 3 nm, with a large number of vacancies in the host layers. Fourier transformed XAFS functions show that the Co−O and Co••••Co coordination numbers (5.5 and 2.8, respectively) in the hybrid CoAl-ELDH/GO material are significantly lower than the corresponding values in bulk CoAl-LDHs (6.0 and 3.8, respectively). Furthermore, in addition to the oxygen vacancies (VO) and cobalt vacancies (VCo), CoAl-ELDH/GO also contains negatively charged VCo−Co−OH δ− sites and exposed lattice oxygen sites. CoAl-ELDH/GO shows excellent performance as a catalyst for the aerobic oxidation of benzyl alcohol, with a TOF of 1.14 h − 1 ; this is nearly five times that of the unexfoliated bulk CoAl-LDHs (0.23 h − 1) precursor. O2-TPD and DRIFT spectroscopy declare that the oxygen storage capacity and mobility are facilitated by the oxygen vacancies and surface lattice oxygen sites. Meanwhile, DFT calculations of adsorption energy show that benzyl alcohol is strongly adsorbed on the oxygen vacancies and negatively charged VCo−Co−OH δ− sites. A kinetic isotope e ect study further illustrates that the vacancy-rich CoAl-ELDH/GO catalyst accelerates the cleavage of the O−H bond in benzyl alcohol. Finally, we show that the hybrid CoAl-ELDH/GO material exhibits excellent catalytic activity and selectivity in the oxidation of a range of other benzylic and unsaturated alcohols.