Photoelectrochemical (PEC) devices that use semiconductors to absorb solar light for water splitting offer a promising way toward the future scalable production of renewable hydrogen fuels. However, the charge recombination in the photoanode/electrolyte (solid/liquid) junction is a major energy loss and hampers the PEC performance from being efficient. Here, we show that this problem is addressed by the conformal deposition of an ultrathin p-type NiO layer on the photoanode to create a buried p/n junction as well as to reduce the charge recombination at the surface trapping states for the enlarged surface band bending. Further, the in situ formed hydroxyl-rich and hydroxyl-ion-permeable NiOOH enables the dual catalysts of CoO(x) and NiOOH for the improved water oxidation activity. Compared to the CoO(x) loaded BiVO4 (CoO(x)/BiVO4) photoanode, the ∼6 nm NiO deposited NiO/CoO(x)/BiVO4 photoanode triples the photocurrent density at 0.6 V(RHE) under AM 1.5G illumination and enables a 1.5% half-cell solar-to-hydrogen efficiency. Stoichiometric oxygen and hydrogen are generated with Faraday efficiency of unity over 12 h. This strategy could be applied to other narrow band gap semiconducting photoanodes toward the low-cost solar fuel generation devices.

Although the nanoporous BiVO 4 photoanode does not fulfi l all criteria from the perspective of practical tandem-electrode applications, it manifested the effectiveness of nanostructuring and represented a more facile approach, compared with gradient doping and heterojunction formation, for electronhole separation. Nanostructuring is essential for performance enhancement for many energy conversion semiconducting materials with relatively poor carrier dynamics, such as hematite [22][23][24] and tantalum nitride. [ 25 ] To seek for the champion nanostructure, however, is a very demanding task. Such strong linkage between nanostructure and performance should also exist for BiVO 4 . We argue that those obstacles to front illumination performance could also be overcome by nanostructure perfection.Here, we demonstrate that largely enhanced front-illumination performance along with improved charge separation efficiency and light transmittance can be realized simultaneously via appropriate nanostructuring and sophisticated morphology control for nondoped nanostructured BiVO 4 electrodes. We also explored the use of a bimetallic NiFe-(oxy)hydroxide/borate (NiFeO x -B i ) oxygen evolution catalyst (OEC) as a cocatalyst for BiVO 4 electrodes to make the best of the outstanding charge separation capability for water splitting. As a result, the solar energy conversion effi ciency exceeded 2% for the fi rst time for BiVO 4 based photoanodes. Moreover, such an effi ciency was achieved under front illumination, together with a transmittance larger than 50% above 600 nm wavelength, making our electrode a perfect candidate for tandem applications.Our BiVO 4 electrode possesses a characteristic worm-like network morphology, with an optimized diameter of the nanostructure unit ≈120 nm ( Figure 2 f). Its monoclinic scheelite crystal structure was confi rmed by X-ray diffraction (XRD) ( Figure S4, Supporting Information). To distinguish from the reported nanoporous BiVO 4 electrode, it will be referred as nanoworm BiVO 4 electrode hereafter. A two-step approach was used for its preparation, similar to that used for the synthesis of nanoporous BiVO 4 electrode. A BiOI fl ake precursor was fi rst prepared by electrodeposition on an indium tin oxide (ITO) substrate, followed with addition of vanadyl acetyl acetonate dissolved in dimethyl sulfoxide (DMSO) and annealing in air. The thermally stable ITO glass from GEOMATEC has a much smoother surface and is more conductive (5 Ω sq −1 ) compared with most fl uorine-doped tin oxide (FTO) glasses, so that the voltage loss can be minimized. Our new process for BiOI deposition involved the use of a more diluted Bi 3+ solution and was more acidic, resulting in a much denser packing of BiOI 2D fl akes on ITO substrate (Figure 2 d). Owing to its increased packing density and also the surface smoothness of ITO, the deposited BiOI layer tended to peel off during deposition,

No abstract

An electrodeposited Cu2ZnSnS4 (CZTS) compact thin film modified with an In2S3/CdS double layer and Pt deposits (Pt/In2S3/CdS/CZTS) was used as a photocathode for water splitting of hydrogen production under simulated sunlight (AM 1.5G) radiation. Compared to platinized electrodes based on a bare CZTS film (Pt/CZTS) and a CZTS film modified with a CdS single layer (Pt/CdS/CZTS), the Pt/In2S3/CdS/CZTS electrode exhibited a significantly high cathodic photocurrent. Moreover, the coverage of the In2S3 layer was found to be effective for stabilization against degradation induced by photocorrosion of the CdS layer. Bias-free water splitting with a power conversion efficiency of 0.28% was achieved by using a simple two-electrode cell consisting of the Pt/In2S3/CdS/CZTS photocathode and a BiVO4 photoanode.

Photoelectrochemical (PEC) water oxidation by semiconductor photoanodes plays a fundamental role for sustainable solar fuel and chemical production. Advanced surface and interface engineering has been demonstrated to be of critical importance for the development of highly efficient and stable water oxidation photoanodes. In this review, we briefly introduce the fundamentals and some general considerations in the development and evaluation of water oxidation photoanodes and the assembly of PEC cells. We summarize several most important roles of surface and interface engineering identified in improving the PEC performance of photoanodes and highlight the most prominent research advancements in these fields. Finally, the outlook for the future development of surface and interface engineering for practical photoelectrochemical water oxidation is concisely discussed.

Optimization of CBM offset boosted hydrogen evolution from water on CuIn1−xGaxSe2 (CIGS) photocathode surface modified with Pt and CdS under simulated sunlight.

A novel small-molecule acceptor, (2,2'-((5E,5'E)-5,5'-((5,5'-(4,4,9,9-tetrakis(5-hexylthiophen-2-yl)-4,9-dihydro-s-indaceno[1,2-b:5,6-b']dithiophene-2,7-diyl)bis(4-(2-ethylhexyl)thiophene-5,2-diyl))bis(methanylylidene)) bis(3-hexyl-4-oxothiazolidine-5,2-diylidene))dimalononitrile (ITCN), end-capped with electron-deficient 2-(3-hexyl-4-oxothiazolidin-2-ylidene)malononitrile groups, is designed, synthesized, and used as the third component in fullerene-free ternary polymer solar cells (PSCs). The cascaded energy-level structure enabled by the newly designed acceptor is beneficial to the carrier transport and separation. Meanwhile, the three materials show a complementary absorption in the visible region, resulting in efficient light harvesting. Hence, the PBDB-T:ITCN:IT-M ternary PSCs possess a high short-circuit current density (J ) under an optimal weight ratio of donors and acceptors. Moreover, the open-circuit voltage (V ) of the ternary PSCs is enhanced with an increase of the third acceptor ITCN content, which is attributed to the higher lowest unoccupied molecular orbital energy level of ITCN than that of IT-M, thus exhibits a higher V in PBDB-T:ITCN binary system. Ultimately, the ternary PSCs achieve a power conversion efficiency of 12.16%, which is higher than the PBDB-T:ITM-based PSCs (10.89%) and PBDB-T:ITCN-based ones (2.21%). This work provides an effective strategy to improve the photovoltaic performance of PSCs.

Vinylene/olefin-linked two-dimensional covalent organic frameworks (v-2D-COFs) have emerged as advanced semiconducting materials with excellent in-plane conjugation, high chemical stabilities, and precisely tunable electronic structures. Exploring new linkage chemistry for the reticular construction of v-2D-COFs remains in infancy and challenging. Herein, we present a solid-state benzobisoxazole-mediated aldol polycondensation reaction for the construction of two novel isomeric benzobisoxazole-bridged v-2D-COFs (v-2D-COF-NO1 and v-2D-COF-NO2) with trans and cis configurations of benzobisoxazole. Interestingly, the isomeric benzobisoxazole linkers endow the two v-2D-COFs with distinct optoelectronic and electrochemical properties, ranging from light absorption and emission to charge-transfer properties. When employed as the photocathode, v-2D-COF-NO1 exhibits a photocurrent of up to ∼18 μA/cm2 under AM 1.5G irradiation at −0.3 V vs reversible hydrogen electrode (RHE), which is twice the value of v-2D-COF-NO2 (∼9.1 μA/cm2). With Pt as a cocatalyst, v-2D-COF-NO1 demonstrates a photocatalytic hydrogen evolution rate of ∼1.97 mmol h–1 g–1, also in clear contrast to that of v-2D-COF-NO2 (∼0.86 mmol h–1 g–1) under identical conditions. This work demonstrates the synthesis of v-2D-COFs via benzobisoxazole-mediated aldol polycondensation with isomeric structures and distinct photocatalytic properties.