Dongdong Qin

Improving the efficiency of water splitting in dye-sensitized solar cells by using a biomimetic electron transfer mediator

Photoelectrochemical water splitting directly converts solar energy to chemical energy stored in hydrogen, a high energy density fuel. Although water splitting using semiconductor photoelectrodes has been studied for more than 40 years, it has only recently been demonstrated using dye-sensitized electrodes. The quantum yield for water splitting in these dye-based systems has, so far, been very low because the charge recombination reaction is faster than the catalytic four-electron oxidation of water to oxygen. We show here that the quantum yield is more than doubled by incorporating an electron transfer mediator that is mimetic of the tyrosine-histidine mediator in Photosystem II. The mediator molecule is covalently bound to the water oxidation catalyst, a colloidal iridium oxide particle, and is coadsorbed onto a porous titanium dioxide electrode with a Ruthenium polypyridyl sensitizer. As in the natural photosynthetic system, this molecule mediates electron transfer between a relatively slow metal oxide catalyst that oxidizes water on the millisecond timescale and a dye molecule that is oxidized in a fast light-induced electron transfer reaction. The presence of the mediator molecule in the system results in photoelectrochemical water splitting with an internal quantum efficiency of approximately 2.3% using blue light.

Reduced monoclinic BiVO4 for improved photoelectrochemical oxidation of water under visible light

A monoclinic BiVO4 film was grown on a transparent conducting substrate for photoelectrochemical oxidation of water. A photocurrent up to 2.3 mA cm(-2) under visible light (λ > 420 nm) was achieved after treating the sample simply by electrochemical reduction followed by NaBH4. The high photocurrent is believed to be due to the improved carrier separation and transportation as a result of increased donor density.

Sn-doped hematite films as photoanodes for efficient photoelectrochemical water oxidation

Sn-doped hematite films were electrochemically deposited on a fluorine-doped tin oxide substrate for use as an anode for photoelectrochemical water oxidation. A high photocurrent of ∼2.8 mA cm−2 at 1.24 V vs. RHE and a conversion efficiency of 0.24% are achieved.

Fe2PO5-Encapsulated Reverse Energetic ZnO/Fe2O3 Heterojunction Nanowire for Enhanced Photoelectrochemical Oxidation of Water

Zinc oxide is regarded as a promising candidate for application in photoelectrochemical water oxidation due to its higher electron mobility. However, its instability under alkaline conditions limits its application in a practical setting. Herein, we demonstrate an easily achieved wet-chemical route to chemically stabilize ZnO nanowires (NWs) by protecting them with a thin layer Fe2 O3 shell. This shell, in which the thickness can be tuned by varying reaction times, forms an intact interface with ZnO NWs, thus protecting ZnO from corrosion in a basic solution. The reverse energetic heterojunction nanowires are subsequently activated by introducing an amorphous iron phosphate, which substantially suppressed surface recombination as a passivation layer and improved photoelectrochemical performance as a potential catalyst. Compared with pure ZnO NWs (0.4 mA cm-2 ), a maximal photocurrent of 1.0 mA cm-2 is achieved with ZnO/Fe2 O3 core-shell NWs and 2.3 mA cm-2 was achieved for the PH3 -treated NWs at 1.23 V versus RHE. The PH3 low-temperature treatment creates a dual function, passivation and catalyst layer (Fe2 PO5 ), examined by X-ray photoelectron spectroscopy, TEM, photoelectrochemical characterization, and impedance measurements. Such a nano-composition design offers great promise to improve the overall performance of the photoanode material.

Self-supported rectangular CoP nanosheet arrays grown on a carbon cloth as an efficient electrocatalyst for the hydrogen evolution reaction over a variety of pH values

Recent research suggests that transition metal phosphides (TMPs) are one of the most promising nobel-metal-free electrocatalysts for catalyzing the hydrogen evolution reaction. In this study, we report rectangular CoP nanosheet (NS) arrays on carbon cloth (CoP NS/CC) via a concise two-step synthetic method. The 3D rectangular CoP NS/CC with a three-dimensional porous and self-supported structure was fabricated via a hydrothermal method, followed by a low-temperature phosphidation treatment. Such 3D rectangular CoP NS/CC, as an HER electrocatalyst in acidic solution, exhibited high activity, good stability, and nearly 100% Faradaic efficiency (FE). The electrocatalyst requires an overpotential of 92, 112 and 195 mV to achieve current densities of 10, 20 and 100 mA cm−2, respectively, and maintain its catalytic stability for more than 50 h. In addition, the electrocatalyst works well in a neutral environment.

Phosphorus-doped TiO2 nanotube arrays for visible-light-driven photoelectrochemical water oxidation

Phosphorus-doped TiO2 nanotube arrays have been prepared via a phosphine annealing protocol and have been found to be efficient towards visible-light-driven water oxidation. Optimal visible light photocurrents of 0.25 mA cm−2 at 1.23 V and 0.85 mA cm−2 at 2.0 V vs. the RHE are achieved, which are the best reported values for phosphorus-doped TiO2.

A nanostructured hematite film prepared by a facile “top down” method for application in photoelectrochemistry

To overcome tough conditions currently used for the preparation of nanostructured hematite films on a conducting substrate, a rational and easy method of chemical etching involving Fe3+ release and material growth in the presence of OH- has been developed. By carefully tuning the parameters influencing the morphologies of hematite, including the synthetic procedure, the concentration of etching solution, temperature, etching time and the morphology controlling surfactant, hematite films grown on iron foil with various morphologies (e.g. nanorod, nanowire, ultrathin nanoflake and cauliflower-like shape) have been achieved. In particular, it is found that F- is an effective surfactant to control the morphology as well as the crystallization process of hematite. Ultrathin nanoflakes having a minimized feature size exhibit the best photocurrent of 0.5 mA cm-2 (1.23 V vs. RHE, RHE is reversible hydrogen electrode) among the samples tested as a result of facilitated hole diffusion to the electrolyte and thus lowered carrier recombination. Compared with pristine hematite, a nearly tripled photocurrent is observed when H2O2 is added in the electrolyte as a hole scavenger, suggesting the presence of a charge injection barrier in the surface of samples. According to this, the strategy of Co2+ treatment is utilized and the improved photocurrent is seen, likely due to the improved water oxidation kinetics and surface state passivation. We believe that this convenient and economical method can be extended to the synthesis of other alkaline metal oxide nanomaterials as long as the redox potential of S2O82-/SO42- is higher than Mn+/M (M refers to metal).

Cathodic electrochemiluminescence of a CdSe/ZnS QDs-modified glassy carbon electrode and its application in sensing of Pb2+

This paper reports the electrochemiluminescence (ECL) behavior of CdSe/ZnS with K2S2O8 as the coreactant. The effects of pH, K2S2O8 concentration, the duration of the reaction of 4-ATP with GCE and the duration of the reaction of 4-ATP/GCE with QDs on ECL intensity were studied in detail. A possible ECL reaction mechanism was then proposed. In addition, it was observed that the ECL intensity was efficiently quenched by trace amounts of heavy metal ion. Based on the quenching effect of Pb2+ upon the ECL of CdSe/ZnS QDs, a QDs-ECL sensor was constructed to detect Pb2+ in preserved duck egg. The sensor showed good reproducibility and stability.

A simple fluorescence sensor for the detection of nitrite (NO2−) in real samples using water-dispersible graphite-like carbon nitride (w-g-C3N4) nanomaterials

A novel strategy was developed for the fluorescence detection of nitrite (NO2−) in real samples. The method is based on the reaction of water-dispersible graphite-like carbon nitride (w-g-C3N4) with nitrite (NO2−) in an acidic medium to form a new kind of weak fluorescence species. Under optimal conditions, the limit of detection (LOD) for nitrite (NO2−) detection was determined to be 0.16 nM (S/N = 3), and the relative fluorescence intensity versus logarithm concentration of nitrite (NO2−) showed good linearity in the range from 0 to 58.5 μM with R2 = 0.997. This probe displayed several appealing properties including low-cost, simplicity and convenience, high sensitivity, and excellent selectivity.

Investigation of proton-driven amine functionalized tube array as ion responsive biomimetic nanochannels

A simple amine embellished tube array was assembled at the liquid–liquid interface to study ion transfer behavior. Variation in the pH of the solution resulted in three different protonation states at the amino groups of the nanochannel, which in turn regulated ion transport, similar to the switching effect of ion channels in vivo.