The light harvesting effects along with the energy barrier properties in dye sensitized solar cells (DSSCs) have been studied by utilizing an easily synthesizable and costeffective nanocube assembled micron-sized SrTiO 3 (STO NCMS) in a binary hybrid photoanode with ZnO nanoparticles. An optimized photoanode loaded with 3% STO NCMS yielded a ∼2-fold increment in power conversion efficiency compared to pristine ZnO NP based device. Improved performance of photoanode with hybrid composite scaffold can be accredited to the boosted optical response in conjunction with impeded reverse tunneling probability of STO NCMS containing photoanode. Micron-sized STO NCMS provides a better light absorption in the photoanodes owing to optical confinement of incident light by multiple reflections generated from mirror-like facets of SrTiO 3 nanocubes as well as enhanced light scattering effects from individual entity. IPCE analysis revealed a better absorption of low energy photons that in turn resulted in enhanced solar to electricity generation for an optimized ratio of STO NCMS. An effective photoinduced charge separation has been achieved with a uniquely aligned band structure, resulting in enhanced power conversion efficiency. Electrochemical impedance analysis unveiled that incorporation of STO NCMS can effectively prolong the lifetime of photo-injected electrons (τ e ) as well as a higher value of recombination resistance (R rec ) at the semiconductor/ dye/electrolyte heterointerface indicating an impeded reverse tunneling probability of photoinjected electrons.

The design of a photoanode with a bridging strategy that can enhance the charge injection and transport in a heterojunction can be an efficient approach to separate the photogenerated charge carriers and enhance the water oxidation kinetics. Aiming at such issues, herein we propose a BiVO4/GQDs/CoSn-LDH (layered double hydroxide) photoanode, which leads to the formation of a p–n heterojunction with bridged graphene quantum dots (GQDs) to accelerate the photoelectrochemical (PEC) performance. The BiVO4/GQDs/CoSn-LDH photoanode exhibits a maximum photocurrent density of 4.15 mA/cm2, which is ∼3-fold higher than for the pristine BiVO4 photoanode with an ∼250 mV cathodic shift in the onset potential. A faradaic yield of ∼91% confirms that the obtained photocurrent is mainly due to water oxidation. A mechanistic study based on the electrochemical impedance (EIS), charge separation, and charge injection efficacy measurements reveals that the introduction of GQDs between BiVO4 and CoSn-LDH provides a continuous conducting network to extract holes from the BiVO4 surface and efficiently inject into the CoSn-LDH surface for the water oxidation reaction.

In this work, a noble metal-free one-dimensional Co(OH)F and hierarchical BiVO 4 combination as a model system is proposed for an efficient photoelectrochemical catalyst. BiVO 4 , known for its superior theoretical current density of 7.5 mA/cm 2 , suffers from poor photoelectrochemical performance due to the sluggish water oxidation kinetics, recombination of photogenerated carriers, and results in reduced photoelectrochemical water oxidation. BiVO 4 /Co(OH)F photoanode exhibits an enhanced photocurrent and a cathodic shift of 160 mV in onset potential as compared to the pristine BiVO 4 photoanode. Cyclic voltametric studies reveal that cobalt exists in the mixed valence state. The presence of fluorine by virtue of its high electronegativity induces facile positive charge on the metal center, i.e., on cobalt, thereby Co 2+ ions as an active site accept holes more efficiently from the semiconductor and oxidized to Co 3+ or/and Co 4+ . Subsequently, these active species, Co 3+ or/and Co 4+ , deliver the positive charge to produce O 2 and recover to the initial state to regenerate redox couple. A mechanistic study reveals that Co(OH)F nanorods as an efficient hole extractor by virtue of its redox ability, suppresses the recombination of photogenerated electron−hole at the electrolyte/semiconductor interface and accelerates the water-oxidation kinetics. Co(OH)F modification of the BiVO 4 surface is able to utilize a higher number of holes, which have reached the semiconductor/electrolyte interface for water oxidation that resulted in a photocurrent of 3.4 mA/cm 2 . Investigations on the hole transfer efficiency reveals a faster oxidation kinetics, resulting in improved charge injection in the presence of Co(OH)F. Electrochemical impedance measurements shows a low interfacial charge transfer resistance leading to better photoelectrochemical performance. A Faradaic yield of ∼95% suggests that the generated charge carriers (anodic photocurrent) in the BiVO 4 /Co(OH)F photoanode is predominantly due to water oxidation.

Photoelectrochemical (PEC) water oxidation, a desirable strategy to meet future energy demands, has several bottlenecks to resolve. One of the prominent issues is the availability of charge carriers at the surface reaction site to promote water oxidation. Of the several approaches, metal dopants to enhance the carrier density of the semiconductors, is an important one. In this work, we have studied the effect of In-doping on monoclinic WO 3 nanoblocks, growing vertically over fluorine-doped tin oxide (FTO) without the aid of any seed layer. X-ray photoelectron spectroscopy (XPS) data reveals that In 3 + ions are partially occupying the W 6 + ions in In-doped WO 3 photoanode. In 3 + ions are offering better performance by adding additional charge carriers for amplifying the expression of the number of carriers. The maximum current density value of 2.18 mA/cm 2 has been provided by the optimized In-doped WO 3 photoanode with 3 wt% indium doping at 1.23 V vs. RHE, which is~3 times higher than that of undoped monoclinic WO 3 photoanode. Mott-Schottky (MS) analysis reveals charge carrier density (N D) for In-doped WO 3 photoanode has been enhanced by a factor of 3. An average Faradic yield of~90 percent has been achieved which can serve as a model system using In 3 + as a dopant for an inexpensive and attractive method for enhanced WO 3 based PEC water oxidation.

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