The BiVO4 photoelectrochemical (PEC) electrode in tandem with a photovoltaic (PV) cell has shown great potential to become a compact and cost‐efficient device for solar hydrogen generation. However, the PEC part is still facing problems such as the poor charge transport efficiency owing to the drag of oxygen vacancy bound polarons. In the present work, to effectively suppress oxygen vacancy formation, a new route has been developed to synthesize BiVO4 photoanodes by using a highly oxidative two‐dimensional (2D) precursor, bismuth oxyiodate (BiOIO3), as an internal oxidant. With the reduced defects, namely the oxygen vacancies, the bound polarons were released, enabling a fast charge transport inside BiVO4 and doubling the performance in tandem devices based on the oxygen vacancy eliminated BiVO4. This work is a new avenue for elaborately designing the precursor and breaking the limitation of charge transport for highly efficient PEC‐PV solar fuel devices.

Functional substructures towards artificial light trapping hierarchies inspired by the natural photosynthesis system.

A photo-enhanced Zn–air battery with simultaneous highly efficient in situ H2O2 generation for wastewater treatment was constructed.

There is increasing evidence that defects such as oxygen vacancies are a double‐edged sword for photoelectrochemical (PEC) water splitting. Although surface oxygen vacancies can largely improve the catalytic activity, their bulk counterparts may bind polarons, drag down the carrier transport, and thus degrade the PEC performance. However, it is very challenging to precisely control the spatial and energy distributions of defects. Instead, the infrared part of sunlight, normally discarded in PEC water splitting, is harvested to thermally activate the polarons. With the prototypical BiVO4 photoanode (absorbs blue–ultraviolet light), even when is undoped, a high solar‐to‐hydrogen efficiency of 5.3% is achieved in conjunction with a photothermal substrate (absorbs infrared light) and in tandem with a perovskite solar cell (absorbs red–green). Detailed characterizations reveal that the temperature increase of the system can not only accelerate the polaron hopping, but also activate the polarons bound by defects. This study, by demonstrating the use of the PEC‐inactive infrared part of sunlight to enhance transport kinetics at the device level, allows for panchromatic sunlight harvesting to improve the overall PEC performance.

Fabrication of high-performance tandem cell for solar-assisted water cleavage requires an efficient photoanode with excellent bulk charge separation and surface injection. In light of that, we developed a hybrid photoanode using visible light absorber as main scaffold, a thin layer In 2 O 3 middle layer to enhance charge separation in bulk and finally an active CoOOH catalyst as outer decoration for better surface charge injection. Bulk separation was mainly augmented by In 2 O 3 addition, while the addition of CoOOH largely advanced photocurrent onset and elevated injection efficiency. The resultant photoanode delivered a high current density at low applied bias, showing promising prospect for incorporation into tandem cell for solar-assisted water electrolysis.

oxide (FTO) hexagonal nanocone and nanospikes, [7,8] and also Cui and Xiao et al. have deposited nanoporous Mo-doped bismuth vanadate (Mo:BiVO 4 ) on an engineered cone-shaped nanostructure to form inverse nanocone array BiVO 4based photoanodes. [9,10] These works deposited a thin photoactive material on a 3D conductive substrate constructed by various complicated methods to shorten charge transport distance and enhance light absorption. Scientific analysis with experiments and modeling showed that these 3D nanophotonic structures can "trap" the incident light to the near-surface region and extend the absorption region to 800 nm and even above.However, the maximum absorption wavelength, below which the corresponding photon energy can be absorbed and converted into electron-hole pairs by photoelectrode, is dependent on the bandgap of the specific photoactive materials. [11,12] Therefore the enhanced light trapping beyond the maximum absorption wavelength can be detrimental in a series-connected photocathode and photoanode tandem system or a PEC-photovoltaic (PEC-PV) tandem device, since it will only greatly weaken or even eliminate the light available to the narrow-bandgap material and thus bring down the solar-to-hydrogen (STH) efficiency. Some works attempted to distribute the solar band to advantage by splitting standard AM 1.5 irradiation into two light beams with an additional splitter, but this means a higher cost and more complex equipment hindering practical application. [8,9] At the same time, Constructing 3D nanophotonic structures is regarded as an effective means to realize both efficient light absorption and efficient charge separation. However, most of the 3D structures reported so far enhance light trapping beyond the absorption onset wavelength, and thus greatly attentuate or even completely block the long-wavelength light, which could otherwise be efficiently absorbed by narrow-bandgap materials in a Z-scheme or tandem device. In addition, constructing a 3D conductive substrate often involves complex processes causing increased cost and upscaling problems. To overcome these shortcomings, a novel 3D hematite nanorod@nanobowl array nanophotonic structure is designed and fabricated by a low-cost method. This unique structure can enhance light absorption with tunable cutoffs and rationally concentrate photons right above the bowl bottom, enabling efficient charge separation. By loading NiFeO x as a cocatalyst, a high photocurrent density of 3.41 ± 0.2 mA cm −2 at 1.23 V versus reversible hydrogen electrode (RHE) can be obtained, which is 2.35 times that with a planar structure in otherwise the same system. Water SplittingThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.

The BiVO4 photoelectrochemical (PEC) electrode in tandem with a photovoltaic (PV) cell has shown great potential to become a compact and cost‐efficient device for solar hydrogen generation. However, the PEC part is still facing problems such as the poor charge transport efficiency owing to the drag of oxygen vacancy bound polarons. In the present work, to effectively suppress oxygen vacancy formation, a new route has been developed to synthesize BiVO4 photoanodes by using a highly oxidative two‐dimensional (2D) precursor, bismuth oxyiodate (BiOIO3), as an internal oxidant. With the reduced defects, namely the oxygen vacancies, the bound polarons were released, enabling a fast charge transport inside BiVO4 and doubling the performance in tandem devices based on the oxygen vacancy eliminated BiVO4. This work is a new avenue for elaborately designing the precursor and breaking the limitation of charge transport for highly efficient PEC‐PV solar fuel devices.

Herein, it is demonstrated that gradient Ti doping coupled with an overlayer of NiFeOx on hematite can markedly improve the photoelectrochemical (PEC) water‐splitting efficiency of hematite‐based photoanodes, which are prized from sustainability considerations but have met daunting challenges. First, the gradient Ti doping of hematite has effectively lowered the onset potential while maintaining the high efficiency of photo‐generated charge separation and transmission. Second, the NiFeOx layer not only substantially reduces the surface trap states, but also significantly enhances the oxygen evolution kinetics of hematite‐based photoanodes as an oxygen evolution catalyst, resulting in a further improvement of the onset potential. Consequently, with the TiO2 layer and a double electrode stack design, a remarkable photocurrent density of 4.49 mA cm−2 is achieved at 1.23 V versus reversible hydrogen electrode (RHE) for NiFeOx/(Grad Ti)‐Fe2O3/TiO2 photoanode without any hole scavenger, delivering a high applied bias photo‐to‐current efficiency of up to 0.58% at 1 V versus RHE. This multipronged attack for improving PEC water‐splitting efficiency revitalizes the great promise of hematite photoanodes and sheds light on the design and development of the next‐generation photoelectrodes.