Environment-Benign Colloidal Quantum Dots-Modified Dual Photoelectrodes for Self-Biased Photoelectrochemical Water Splitting

Photoelectrochemical (PEC) water splitting based on colloidal quantum dots (QDs) presents a promising approach for utilizing solar energy to produce green hydrogen energy. Previous research has been mainly focused on the single-photoelectrode QDs-PEC device operated under external bias, while the investigation of dual-photoelectrode configuration for self-biased QDs-PEC system is still lacking. In this work, two types of eco-friendly Cu-AISe/ZnSe:Cu (CZAC) and Mn-AIS/ZnS@Cu (MAZC) QDs were used to respectively sensitize the semiconductor n-type TiO2 and p-type Cu2O photoelectrodes, which acted as the photoanode and photocathode to build a heavy metal-free QDs-based bias-free solar water splitting cell, yielding a maximum photocurrent density of 0.47 mA cm-2 and a solar-to-hydrogen (STH) efficiency of 0.4 % under 1 sun AM 1.5G illumination (100 mW cm-2). Moreover, approximate 692 nmol of H2 and 355 nmol of O2 with molar ratio of ~2 : 1 was detected after two hours of continuous light illumination, demonstrating the effective overall water splitting. This work indicates a significant advancement towards the realization of a cost-effective, efficient and "green" QDs-based artificial solar-to-fuel conversion system.

Dual Heterogeneous Structures Promote Electrochemical Properties and Photocatalytic Hydrogen Evolution for Inverse Opal ZnO/ZnS/Co3O4 Crystals

Potocatalytic hydrogen evolution represnets a promising way to achieve renewable energy sources. Dual heterojunctions with an inverse opal structure are proposed for addressing fundamental challenges (low surface area, inefficient light absorption, and poor charge separation) in photocatalytic water splitting. Inverse opal structure and Co3O4 were introduced to design and synthesize a ZnO/ZnS/Co3O4 (IO-ZnO/ZnS/Co3O4) photocatalyst. Morphology characterizations and photoelectric measurements reveal that the introduction of three-dimensional (3D) structures and dual heterojunctions improves light utilization efficiency and accelerates charge separation, greatly promoting photoelectric performance. The as-prepared IO-ZnO/ZnS/Co3O4 manifests superior photocurrent density (0.49 mA/cm2), which is 4 times higher than that of IO-ZnO/ZnS due to the existence of dual heterojunctions. The result is further confirmed by an enhanced H2 production rate (153.01 μmol/g/h) in pure water. Notably, excellent cycling stability is achieved in pure water because Co3O4 can rapidly capture photogenerated holes to inhibit severe photocorrosion of ZnO/ZnS. Therefore, this work presents a new insight into inhibiting photocorrosion of metal sulfides and promoting their photoelectric performance by combining 3D structures and dual heterojunctions.

Turning off the “shunt channel” by coating with CoFe layered double hydroxide nanocrystals for efficient photoelectrocatalytic water splitting

Tiny and crystalline CoFe(C) nanoparticles can close the “shunt channel” between the cocatalyst and the substrate, and the recombination of photogenerated charge caused by back-reaction is inhibited.

Synthesis and control strategies of nanomaterials for photoelectrochemical water splitting

Photoelectrochemical water splitting to produce hydrogen using solar energy can capture and directly convert solar energy into chemical energy, which is an effective way to deal with the current energy and environmental problems. The conversion efficiency of solar energy depends on the performance of semiconductor photoelectrodes in photoelectrochemical water splitting. This article presents our recent advances in the design and performance control of high-efficiency photoelectrocatalytic materials, followed by the discussion of the strategies employed for improving the performances of photoelectrodes in terms of photon absorption, charge separation and migration, as well as surface chemical reactions.

ZnO nanoparticles supported on dendritic fibrous nanosilica as efficient catalysts for the one-pot synthesis of quinazoline-2,4(1H,3H)-diones

The transmutation of waste into valuable materials has a special place in green chemistry. Herein, we report the preparation of quinazoline-2,4(1H,3H)-diones from 2-iodoaniline, isocyanides, and carbon dioxide in the presence of ZnO NPs stably placed on the surface of dendritic fibrous nanosilica by cellulose (DFNS/cellulose-ZnO) as a catalyst. This is a great economic strategy to create three bonds in a one-pot multicomponent reaction step employing functional groups. To prepare the catalyst, the dendritic fibrous nanosilica surface was first activated using cellulose as a substrate to support ZnO NPs. Cellulose acts as a stabilizing and reducing agent for the ZnO nanocatalyst and eliminates the need for a reducing agent. The structure of the prepared DFNS/cellulose-ZnO was examined by various methods, including thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma (ICP). The largest amount of quinazoline-2,4(1H,3H)-diones was obtained under ideal situations in the presence of 5 mg of DFNS/cellulose-ZnO under carbon dioxide (1 atm) utilizing a balloon set at 70 °C for 3 hours. The substance was reused for ten consecutive runs and the quinazoline-2,4(1H,3H)-dione content was more than 92% each time. This indicates the potential for application in the green and economic production of quinazoline-2,4(1H,3H)-diones, especially from low-cost feedstocks.

The transmutation of waste into valuable materials has a special place in green chemistry.

Lead-Free Perovskite Narrow-Bandgap Oxide Semiconductors of Rare-Earth Manganates

Tremendous success has been achieved in photovoltaic (PV) applications, but PV-generated electricity still cannot compete with traditional power in terms of price. Chemically stable and nontoxic all-oxide solar cells made from earth-abundant resources fulfill the requirements for low-cost manufacturing under ambient conditions and thus are promising as the next-generation approach to solar cells. However, the main obstacles to developing all-oxide solar cells are the spectral absorbers. Besides photovoltaics, novel chemically stable, nontoxic, and earth-abundant narrow-bandgap semiconductors are desired for photochemical applications in photodetectors, photoelectrodes, or photocatalysts. Herein, were report novel lead-free perovskite narrow-bandgap rare-earth semiconductors, YMnO3, HoMnO3, ErMnO3, and YbMnO3, which were identified by screening a family of perovskite rare-earth manganates, RMnO3 (R = Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, and Yb). The sharp edge observed in their absorption spectra indicates the existence of band gaps, further confirmed with laser Raman fluorescence spectra. Good periodic on-off photoelectronic response was observed in 8 of the 12 members (i.e., R = La, Pr, Nd, Sm, Gd, Tb, Dy, and Yb). Among them, YbMnO3 is approved as an n-type semiconductor with a direct band gap near 1.35 eV, whose theoretical Shockley-Queisser efficiency is approximately 33.7% for single-p-n-junction solar cells. This work sheds light on exploring stable oxide semiconductors with a narrow band gap for future applications.

Exposing the photocorrosion mechanism and control strategies of a CuO photocathode

A CuO photocathode modified with TiO₂ and Pt displays superior photocorrosion stability in PEC water splitting.

A high-efficiency and stable cupric oxide photocathode coupled with Al surface plasmon resonance and Al2O3 self-passivation

A high-efficiency and stable CuO/Al/Al₂O₃ photocathode for photoelectrochemical water splitting has been successfully synthesized by a facile magnetron sputtering combined with spontaneous oxidation method.