Songcan Wang

An Electrochemically Treated BiVO4 Photoanode for Efficient Photoelectrochemical Water Splitting

BiVO4 films with (040) facet grown vertically on fluorine doped SnO2 (FTO) glass substrates are prepared by a seed-assisted hydrothermal method. A simple electrochemical treatment process drastically enhances the photocatalytic activity of BiVO4 , exhibiting a remarkable photocurrent density of 2.5 mA cm-2 at 1.23 V vs. reversible hydrogen electrode (RHE) under AM 1.5 G illumination, which is approximately 10-fold higher than that of the pristine photoanode. Loading cobalt borate (CoBi) as cocatalyst, the photocurrent density of the BiVO4 photoanode can be further improved to 3.2 mA cm-2 , delivering an applied bias photon-to-current efficiency (ABPE) of 1.1 %. Systematic studies reveal that crystal facet orientation also synergistically boosts both charge separation and transfer efficiencies, resulting in remarkably enhanced photocurrent densities. These findings provide a facile and effective approach for the development of efficient photoelectrodes for photoelectrochemical water splitting.

Strategies for efficient solar water splitting using carbon nitride

Graphitic carbon nitride (g-C3 N4 )-based photocatalysts are promising for photocatalytic water splitting to produce clean solar fuels due to their low cost, suitable band structure and excellent photocatalytic performance. This review focuses on the state-of-the-art progress of the strategies for modifying g-C3 N4 -based photocatalysts toward efficient photocatalytic water splitting. In particular, we highlight the importance of interfacial engineering and nanostructural control to facilitating charge separation and migration. Other strategies including doping and defect engineering are also concisely discussed. Finally, the perspectives on the challenges and future development of g-C3 N4 -based photocatalysts are presented.

A Binder‐Free and Free‐Standing Cobalt Sulfide@Carbon Nanotube Cathode Material for Aluminum‐Ion Batteries

Rechargeable aluminum-ion batteries (AIBs) are considered as a new generation of large-scale energy-storage devices due to their attractive features of abundant aluminum source, high specific capacity, and high energy density. However, AIBs suffer from a lack of suitable cathode materials with desirable capacity and long-term stability, which severely restricts the practical application of AIBs. Herein, a binder-free and self-standing cobalt sulfide encapsulated in carbon nanotubes is reported as a novel cathode material for AIBs. The resultant new electrode material exhibits not only high discharge capacity (315 mA h g-1 at 100 mA g-1 ) and enhanced rate performance (154 mA h g-1 at 1 A g-1 ), but also extraordinary cycling stability (maintains 87 mA h g-1 after 6000 cycles at 1 A g-1 ). The free-standing feature of the electrode also effectively suppresses the side reactions and material disintegrations in AIBs. The new findings reported here highlight the possibility for designing high-performance cathode materials for scalable and flexible AIBs.

New BiVO4 Dual Photoanodes with Enriched Oxygen Vacancies for Efficient Solar-Driven Water Splitting

Bismuth vanadate (BiVO4 ) is a promising photoanode material for photoelectrochemical (PEC) water splitting. However, owing to the short carrier diffusion length, the trade-off between sufficient light absorption and efficient charge separation often leads to poor PEC performance. Herein, a new electrodeposition process is developed to prepare bismuth oxide precursor films, which can be converted to transparent BiVO4 films with well-controlled oxygen vacancies via a mild thermal treatment process. The optimized BiVO4 film exhibits an excellent back illumination charge separation efficiency mainly due to the presence of enriched oxygen vacancies which act as shallow donors. By loading FeOOH/NiOOH as the cocatalysts, the BiVO4 dual photoanodes exhibit a remarkable and highly stable photocurrent density of 5.87 mA cm-2 at 1.23 V versus the reversible hydrogen electrode under AM 1.5 G illumination. An artificial leaf composed of the BiVO4 /FeOOH/NiOOH dual photoanodes and a single sealed perovskite solar cell delivers a solar-to-hydrogen conversion efficiency as high as 6.5% for unbiased water splitting.

Etching treatment of vertical WO3 nanoplates as a photoanode for enhanced photoelectrochemical performance

Vertically grown WO3 nanoplates (WO3NP) were successfully fabricated by a one-step hydrothermal process using citric acid as a structure directing agent. An innovative etching method was developed to obtain increased surface voids, active crystal facets and surface groups simultaneously, which led to a remarkably improved photocurrent density of ∼1.2 mA cm−2 at 1.23 V vs. RHE, compared to 0.97 mA cm−2 of pristine WO3. Incident photon to current efficiency (IPCE) measurements also displayed a substantive increase of photoresponse in the intrinsic absorption range. Interestingly, a lower onset potential can be obtained after etching which is caused by the change of conduction and valence band positions. Moreover, the photoelectrocatalytic activity of WO3 for degrading methylene blue (MB) was also evaluated. This effective design could provide a promising method to enhance the efficiency of photoelectrochemical performance based on WO3 photoanodes.

Review of recent progress in unassisted photoelectrochemical water splitting: from material modification to configuration design

Abstract. Photoelectrochemical (PEC) energy conversion systems have been considered as a highly potential strategy for clean solar fuel production, simultaneously addressing the energy and environment challenges we are facing. Tremendous research efforts have been made to design and develop feasible unassisted PEC systems that can efficiently split water into hydrogen (H2) and oxygen with only the energy input of sunlight. A fundamental understanding of the concepts involved in PEC water splitting and energy conversion efficiency enhancement for solar fuel production is important for better system design. This review gives a concise overview of the unassisted PEC devices with some state-of-the-art progress toward efficient PEC devices for future sustainable solar energy utilization.

Design and synthesis of porous ZnTiO3/TiO2 nanocages with heterojunctions for enhanced photocatalytic H2 production

Despite the tremendous potential applications of hollow micro/nanostructures, their composition has been limited to mainly single chemical compounds. Inspired by recent innovations in the areas of metal organic frameworks (MOFs) and nanocoating, here, we report the rational synthesis of mesoporous ZnTiO3/TiO2 hollow polyhedra (MZTHP) obtained by hydrothermal treatment of zeolitic imidazolate framework-8 (ZIF-8)@TiO2 core–shell polyhedral particles. The subsequent calcination of these particles caused phase transformation from TiO2 to ZnTiO3 and eventually induced the formation of Zn2TiO4. In addition, the fabrication of these hollow structures revealed a way for the preparation of hollow polyhedral photocatalysts with Pt nanoparticles deposited onto their external surface (PHS-1) or encapsulated inside their hollow structures (PHS-2). Importantly, these two types of Pt-decorated nanoparticles are shown to exhibit an improved yet distinctly different performance for photocatalytic hydrogen production, highlighting that the photocatalytic activity correlates with the Pt location and dispersion.

The contribution of functional groups in carbon nanotube electrodes to the electrochemical performance

In this paper, carboxylic acid functionalized and aminated carbon nanotubes (CNTs) were prepared via mixacid treatment and further amination. In comparison with pristine CNTs, the effect of functional groups on the electrochemical properties was investigated. Transmission electron microscopy (TEM) and Fourier transform infrared spectrophotometer (FTIR) suggested that the highly tangled long ropes of CNT were cut into short, open-ended pipes with the corresponding functional groups grafted successfully onto their surfaces. The amount of functional groups was further determined by acid-base titration. Charge-discharge testing and cyclic voltammetry (CV) were used to characterize the electrochemical behaviors of the samples. It is found that the as-received functional groups, especially the carboxylic groups evidently improved the capacities of the electrodes due to the reversible Faradic reaction. Therefore, functionalized CNTs may be the promising material used in lithium ion batteries to deliver both high reversible capacity and high power capability.

Processable graphene oxide-embedded titanate nanofiber membranes with improved filtration performance

Graphene oxide (GO)-embedded titanate nanofiber (TNF) membranes with improved filtration performance are prepared successfully by a two-step method including electrostatic assembly of GO and TNFs into hybrids and subsequent processing of them into membranes by vacuum filtration. The embedded contents of GO sheets in films and thickness of as-assembled films can be adjusted facilely, endowing such composite films with good processability. Owing to the skilful introduction of GO sheets, the pore and/or channel structures in these hybrid membranes are modified. By treating different dye solutions (Direct Yellow and Direct Red), the filtration properties of these membranes show that the introduction of certain amount of GO sheets efficiently improve the separation performance of the membranes. Interestingly, these GO-embedded TNF membranes also display superior selective separation performance on filtrating the mixture solutions of such two dyes, making these hierarchical membranes more flexible and versatile in water treatment areas.

Mesoporous ZnFe2O4 Photoanodes with Template-tailored Mesopores and Temperature-dependent Photocurrents

Mesoporous ZnFe2 O4 photoanodes have been prepared via dip-coating utilizing the evaporation-induced self-assembly of two different block-copolymer templates to investigate the influence of pore geometry on the photoelectrochemcial performance of those earth-abundant photoelectrodes. The use of commercial block copolymers, triblock copolymer Pluronic® F127 and the diblock copolymer PIB3000 as templates, leads to different pore morphologies under identical preparation conditions due to different polymer stabilities. Interestingly, pore morphology in mesoporous ZnFe2 O4 turned out to be less important for the photoelectrochemical performance. Contrary, sufficiently developed crystalline domains gained through optimized temperature treatment resulted in maximum photoelectrochemical performance among the investigated samples. This disproves the necessity of expensive, tailor-made polymer soft templates to synthesize high-performing mesoporous ZnFe2 O4 photoanodes.