Hao-Lin Wu

Self-Assembled Framework Enhances Electronic Communication of Ultrasmall-Sized Nanoparticles for Exceptional Solar Hydrogen Evolution

Colloidal quantum dots (QDs) have demonstrated great promise in artificial photosynthesis. However, the ultrasmall size hinders its controllable and effective interaction with cocatalysts. To improve the poor interparticle electronic communication between free QD and cocatalyst, we design here a self-assembled architecture of nanoparticles, QDs and Pt nanoparticles, simply jointed together by molecular polyacrylate to greatly enhance the rate and efficiency of interfacial electron transfer (ET). The enhanced interparticle electronic communication is confirmed by femtosecond transient absorption spectroscopy and X-ray transient absorption. Taking advantage of the enhanced interparticle ET with a time scale of ∼65 ps, 5.0 mL of assembled CdSe/CdS QDs/cocatalysts solution produces 94 ± 1.5 mL (4183 ± 67 μmol) of molecular H2 in 8 h, giving rise to an internal quantum yield of ∼65% in the first 30 min and a total turnover number of >1.64 × 107 per Pt nanoparticle. This study demonstrates that self-assembly is a promising way to improve the sluggish kinetics of the interparticle ET process, which is the key step for advanced H2 photosynthesis.

Improved Photoelectrocatalytic Performance for Water Oxidation by Earth-Abundant Cobalt Molecular Porphyrin Complex-Integrated BiVO4 Photoanode

An earth-abundant, low-cost cobalt porphyrin complex (CoTCPP) is designed as a molecular catalyst to work on three-dimensional BiVO4 film electrode for water oxidation for the first time. Under illumination of a 100 mW cm(-2) Xe lamp, the CoTCPP-functionalized BiVO4 photoanode exhibits a 2-fold enhancement in photocurrent density at 1.23 V vs RHE and nearly a 450 mV cathodic shift at 0.5 mA cm(-2) photocurrent density relative to bare BiVO4 in 0.1 M Na2SO4 (pH = 6.8). Simultaneously, stoichiometric oxygen and hydrogen are generated with a faradic efficiency of 80% over 4 h. The activity and stability of the BiVO4 photoanode are dramatically increased by molecular CoTCPP, giving rise to higher performance than previously reported noble metal ruthenium complex-modified BiVO4 photoanode. By using hydrogen peroxide as the hole scavenger, we demonstrate that molecular CoTCPP catalyst greatly suppresses the hole-electron recombination on the surface of BiVO4 semiconductor, which offers a promising route toward high efficiency, low cost, practical solar fuel generation device.

Hole-Accepting-Ligand-Modified CdSe QDs for Dramatic Enhancement of Photocatalytic and Photoelectrochemical Hydrogen Evolution by Solar Energy

Solar H2 evolution of CdSe QDs can be significantly enhanced simply by introducing a suitable hole‐accepting‐ligand for achieving efficient hole extraction and transfer at the nanoscale interfaces, which opens an effective pathway for dissociation of excitons to generate long‐lived charge separation, thus improving the solar‐to‐fuel conversion efficiency.

Secondary coordination sphere accelerates hole transfer for enhanced hydrogen photogeneration from [FeFe]-hydrogenase mimic and CdSe QDs in water.

Achieving highly efficient hydrogen (H2) evolution via artificial photosynthesis is a great ambition pursued by scientists in recent decades because H2 has high specific enthalpy of combustion and benign combustion product. [FeFe]-Hydrogenase ([FeFe]-H2ase) mimics have been demonstrated to be promising catalysts for H2 photoproduction. However, the efficient photocatalytic H2 generation system, consisting of PAA-g-Fe2S2, CdSe QDs and H2A, suffered from low stability, probably due to the hole accumulation induced photooxidation of CdSe QDs and the subsequent crash of [FeFe]-H2ase mimics. In this work, we take advantage of supramolecular interaction for the first time to construct the secondary coordination sphere of electron donors (HA−) to CdSe QDs. The generated secondary coordination sphere helps realize much faster hole removal with a ~30-fold increase, thus leading to higher stability and activity for H2 evolution. The unique photocatalytic H2 evolution system features a great increase of turnover number to 83600, which is the highest one obtained so far for photocatalytic H2 production by using [FeFe]-H2ase mimics as catalysts.

Surface stoichiometry manipulation enhances solar hydrogen evolution of CdSe quantum dots

Surface stoichiometry is a sensitive parameter affecting the decay dynamics of photogenerated hole–electron pairs of QDs. However, the effect of this manipulation on artificial photocatalytic H2 evolution is unclear. Here, we report that surface stoichiometry manipulation is a facile and feasible approach for enhancing H2 photogeneration of QDs. In the absence of an external cocatalyst, a decrease in the surface Se ratio of CdSe QDs from ∼16.7% to ∼4.9% gives a more than 10-fold increase in solar H2 evolution. Taking Ni(II) as an external cocatalyst, CdSe QDs with a surface Se ratio of ∼4.9% can produce ∼1600 ± 151 μmol H2 gas during 27 h of visible-light irradiation, giving a total turnover number of (1.24 ± 0.12) × 105 on CdSe QDs and an apparent quantum yield of 10.1%, which is about 8 times that of CdSe QDs with a surface Se ratio of ∼16.7% under the same conditions. Mechanistic insights obtained by a combination of steady-state and time-resolved spectroscopic techniques indicate that surface stoichiometry exerts a significant influence on the exciton kinetics of CdSe QDs: a higher ratio of surface Se would increase the possibility of exciton recombination through hole trapping, thus depressing the performance of solar H2 evolution.

Enhanced Charge Separation Efficiency Accelerates Hydrogen Evolution from Water of Carbon Nitride and 3,4,9,10-Perylene-tetracarboxylic Dianhydride Composite Photocatalyst

The catalytic ability of graphitic carbon nitride is greatly affected by its intrinsic electronic properties. Although combination with chromophore has been demonstrated to be one of the promising approaches to improve the catalytic performance of carbon nitride, it is imperative to understand the key factors governing the whole process. Here, we report a composite photocatalyst CN-P by embedding perylene unit into the matrix of carbon nitride. The composite photocatalyst could catalyze hydrogen evolution with a high rate of 17.7 mmol h-1 g-1, which is 2.8 times faster than pure carbon nitride. The apparent quantum efficiency is high up to be 5.8% at 450 nm. Detailed studies reveal that the light absorption ability and charge separation efficiency are greatly enhanced in the synthesized catalyst. These are the key factors for the improved hydrogen evolution ability of CN-P than that of pure carbon nitride.

Recent Advances in Sensitized Photocathodes: From Molecular Dyes to Semiconducting Quantum Dots

Abstract The increasing demand for sustainable and environmentally benign energy has stimulated intense research to establish highly efficient photo‐electrochemical (PEC) cells for direct solar‐to‐fuel conversion via water splitting. Light absorption, as the initial step of the catalytic process, is regarded as the foundation of establishing highly efficient PEC systems. To make full use of visible light, sensitization on photoelectrodes using either molecular dyes or semiconducting quantum dots provides a promising method. In this field, however, there remain many fundamental issues to be solved, which need in‐depth study. Here, fundamental knowledge of PEC systems is introduced to enable readers a better understanding of this field. Then, the development history and current state in both molecular dye‐ and quantum dot‐sensitized photocathodes for PEC water splitting are discussed. A systematical comparison between the two systems has been made. Special emphasis is placed on the research of quantum dot‐sensitized photocathodes, which have shown superiority in both efficiency and durability towards PEC water splitting at the present stage. Finally, the opportunities and challenges in the future for sensitized PEC water‐splitting systems are proposed.

Direct synthesis of sulfide capped CdS and CdS/ZnS colloidal nanocrystals for efficient hydrogen evolution under visible light irradiation

CdS and CdS/ZnS colloidal nanocrystals (NCs) capped with inorganic sulfide (S2−) ligands were directly synthesized with no aid of organic ligands in water. The obtained CdS/ZnS-S2− NCs show a surprising activity for hydrogen evolution with a rate of 1.61 mmol mg−1 h−1 and an internal quantum yield of 54% under 465 nm light irradiation.

Solar Energy Conversion: Hole-Accepting-Ligand-Modified CdSe QDs for Dramatic Enhancement of Photocatalytic and Photoelectrochemical Hydrogen Evolution by Solar Energy (Adv. Sci. 4/2016)

Water‐splitting by sunlight to produce H2 offers one of the best solutions to meet future energy demands. In order to develop suitable catalysts, L.‐Z. Wu and co‐workers have established a facile approach, detailed in article 1500282, involving simple integration of hole‐accepting ligands onto quantum dots (QDs), to dramatically improve the H2 evolution efficiency from QDs both in aqueous solution and under photoelectrochemical conditions.