Shuang Cao

Ultrafine CoP Nanoparticles Supported on Carbon Nanotubes as Highly Active Electrocatalyst for Both Oxygen and Hydrogen Evolution in Basic Media.

The development of low-cost and highly active electrocatalysts for two half reactions: H2 and O2 evolution reactions (HER and OER), is still a huge challenge to realize water splitting. Herein, we report that CoP nanoparticles (NPs) can act as a bifunctional catalyst for both HER and OER. Particularly, ultrafine CoP NPs decorated on N-doped multiwalled carbon nanotube (MWCNT) exhibit remarkable catalytic performance for OER in 0.1 M NaOH aqueous solution, with a low onset overpotential of 290 mV, a Tafel slope of 50 mV dec(-1), an overpotential (η) of 330 mV at 10 mA cm(-2), and approximately 100% Faradaic efficiency, paralleling the performance of state-of-the-art Co-based OER catalysts including Co3O4, CoSe2, and Co-Pi. The hybrid catalyst is capable of maintaining a high catalytic current density for at least 10 h without any loss of catalytic activity. Meanwhile, the noble-metal-free catalyst also shows good activity and duarability for HER under the same basic condition.

Cobalt phosphide as a highly active non-precious metal cocatalyst for photocatalytic hydrogen production under visible light irradiation

Cobalt phosphide (Co2P) is found, for the first time, to be a novel cocatalyst for efficient photocatalytic hydrogen evolution for a system containing CdS nanorods as a photocatalyst and DL-mandelic acid as an electron donor in water. Under optimal conditions, the H2-production rate can reach up to 19 373 μmolh−1 g−1 after 10 h of LED light irradiation. Meanwhile, DL-mandelic acid can be oxidized to benzoylformic acid by the photo-generated holes of CdS nanorods, providing a green and economic way to synthesize benzoylformic acid from DL-mandelic acid.

Nanostructured Ni2P as a Robust Catalyst for the Hydrolytic Dehydrogenation of Ammonia–Borane

Ammonia-borane (AB) is a promising chemical hydrogen-storage material. However, the development of real-time, efficient, controllable, and safe methods for hydrogen release under mild conditions is a challenge in the large-scale use of hydrogen as a long-term solution for future energy security. A new class of low-cost catalytic system is presented that uses nanostructured Ni2 P as catalyst, which exhibits excellent catalytic activity and high sustainability toward hydrolysis of ammonia-borane with the initial turnover frequency of 40.4 mol(H2)  mol(Ni2P) (-1)  min(-1) under air atmosphere and at ambient temperature. This value is higher than those reported for noble-metal-free catalysts, and the obtained Arrhenius activation energy (Ea =44.6 kJ mol(-1) ) for the hydrolysis reaction is comparable to Ru-based bimetallic catalysts. A clearly mechanistic analysis of the hydrolytic reaction of AB based on experimental results and a density functional theory calculation is presented.

Electrochemical Water Oxidation by In Situ-Generated Copper Oxide Film from [Cu(TEOA)(H2O)2][SO4] Complex

Although many noble-metal oxide catalysts show high activities and low overpotentials for water oxidation, there remain challenges in the sustainable developments of more inexpensive, efficient, and robust catalysts. Here, we report a heterogeneous copper oxide film toward water oxidation formed upon the oxidative polarization of an acetate electrolyte containing Earth-abundant Cu(II) salts in combination with commercially available triethanolamine (TEOA) as the catalyst precursor. A 1:1 molar ratio of TEOA coordinates to Cu(II) is favored in aqueous solution and the single crystal of the complex was obtained. The film has a modest overpotential of 550 mV and the catalytic performance of the material is demonstrated by long-term electrolysis at 1.3 V vs normal hydrogen electrode, a stable current density persists for at least 3 h, and a Faradaic efficiency of almost 100% is obtained.

Incorporation of a [Ru(dcbpy)(bpy)2]2+ photosensitizer and a Pt(dcbpy)Cl2 catalyst into metal–organic frameworks for photocatalytic hydrogen evolution from aqueous solution

A molecular photosensitizer [Ru(dcbpy)(bpy)2]2+ (dcbpy = 2,2′-bipyridyl-5,5′-dicarboxylic acid) and a proton reduction catalyst Pt(dcbpy)Cl2 were successfully incorporated into a highly robust metal–organic framework (MOF) of Zr(IV)6O4(OH)4(bpdc)6 (bpdc = 4,4′-biphenyldicarboxylic acid) by making use of a mix-and-match approach. The molecular integrity of the Ru and Pt complexes within the MOFs was demonstrated by a variety of techniques, including XRD, BET, TGA, SEM, TEM, HAADF-STEM, EDX, DRUS and XPS. This di-component Ru–Pt@UIO-67 MOF assembly allows a facile arrangement of the photosensitizer and the reduction catalyst with close spatial proximity, promotes the electron transfer between them, and thus leads to a significantly improved hydrogen evolution activity in aqueous solution at pH 5.0 upon visible light irradiation. This Ru–Pt@UIO-67 system represents the first example of MOFs functionalized with two different transition metal complexes, which can be used as a photosensitizer and catalyst, respectively, for hydrogen generation from water.

Robustly photogenerating H2 in water using FeP/CdS catalyst under solar irradiation.

Photosplitting water for H2 production is a promising, sustainable approach for solar-to-chemical energy conversion. However, developing low-cost, high efficient and stable photocatalysts remains the major challenge. Here we report a composite photocatalyst consisting of FeP nanoparticles and CdS nanocrystals (FeP/CdS) for photogenerating H2 in aqueous lactic acid solution under visible light irradiation. Experimental results demonstrate that the photocatalyst is highly active with a H2-evolution rate of 202000 μmol h−1 g−1 for the first 5 h (106000 μmol h−1 g−1 under natural solar irradiation), which is the best H2 evolution activity, even 3-fold higher than the control in situ photo-deposited Pt/CdS system, and the corresponding to an apparent quantum efficiency of over 35% at 520 nm. More important, we found that the system exhibited excellent stability and remained effective after more than 100 h in optimal conditions under visible light irradiation. A wide-ranging analysis verified that FeP effectively separates the photoexcited charge from CdS and showed that the dual active sites in FeP enhance the activity of FeP/CdS photocatalysts.

Enhanced photocatalytic H2-evolution by immobilizing CdS nanocrystals on ultrathin Co0.85Se/RGO–PEI nanosheets

We herein report a novel noble-metal-free photocatalytic H2-production system by immobilizing CdS nanocrystals on ultrathin Co0.85Se/graphene nanosheets. The well-designed composite material was prepared by a simple solvothermal method and achieved a dramatically enhanced H2-evolution performance when compared with other bulk counterparts. Under optimal conditions, the H2-evolution efficiency can reach up to 17.60 μmol mg−1 h−1 after 10 h of LED visible light irradiation, which is comparable to that of noble Pt nanoparticles (18.60 μmol mg−1 h−1). It is proposed that the unusual catalytic rate arises from the special nanostructure of Co0.85Se and a positive synergetic effect between Co0.85Se and graphene. The results show that the ultrathin Co0.85Se which possesses a half-metallic character is a promising noble-metal-free cocatalyst for practical photocatalytic hydrogen production application.

Highly selective oxidation of sulfides on a CdS/C3N4 catalyst with dioxygen under visible-light irradiation

A CdS/C3N4 composite photocatalyst was fabricated by a facile method, and its structure, composition, and morphology were characterized in detail. The catalyst exhibited high photocatalytic product selectivity towards the oxidation of sulfides into corresponding sulfoxides even when the irradiation time was extended to 20 h. The synergistic effect between CdS and C3N4 gave rise to efficient interfacial transfer of photogenerated electrons and holes on both materials, as confirmed by transient photocurrent measurements. The best photocatalytic activity for the catalyst prepared at 300 °C was achieved at a C3N4/CdS ratio of 0.3. Sulfides were efficiently oxidized to sulfoxides with dioxygen under visible-light illumination in methanol at room temperature. The conversion efficiency of sulfides with electron-withdrawing groups was lower than those with a donating substituent, and the conversion strongly depended on the steric hindrance effect of the substituent. A possible photocatalytic mechanism was proposed based on electron spin resonance, trapping experiments, and other experimental results.

Metal Phosphides as Co-Catalysts for Photocatalytic and Photoelectrocatalytic Water Splitting

Solar-to-hydrogen conversion based on photocatalytic and photoelectrocatalytic water splitting is considered as a promising technology for sustainable hydrogen production. Developing earth-abundant H2 -production materials with robust activity and stability has become the mainstream in this field. Due to the unique properties and characteristics, transition metal phosphides (TMPs) have been proven to be high performance co-catalysts to replace some of the classic precious metal materials in photocatalytic water splitting. In this Minireview, we summarize the recent significant progress of TMPs as cocatalysts for water splitting reaction with high activity and stability. Firstly, the characteristic of TMPs is briefly introduced. Then, we mainly discuss the recent research efforts toward their application as photocatalytic co-catalysts in photocatalytic H2 -production, O2 -evolution and photoelectrochemical water splitting. Finally, the catalytic mechanism, current existing challenges and future working directions for improving the performance of TMPs are proposed.

Photoreduction of Iron(III) to Iron(0) Nanoparticles for Simultaneous Hydrogen Evolution in Aqueous Solution

Crystalline Fe nanoparticles were obtained with fluorescein (Fl) as the photosensitizer in triethylamine (TEA) or triethanolamine (TEOA) aqueous solution with FeCl3 as the Fe precursor under bright visible-light light-emitting diode (LED) irradiation. Photoinduced electron transfer from excited state Fl* and Fl(-) to Fe(3+) produced the Fe nanoparticles, which served as the active catalyst for in situ photocatalytic hydrogen production with Fl and TEA or TEOA as the photosensitizer and electron donors, respectively, in the same system. Robust hydrogen production activities were observed under the Fe nanoparticle photoreduction conditions in basic solution, and tens of milliliters of hydrogen were obtained over prolonged LED irradiation. If inorganic support materials such as NH2 -MCM-41 or reduced graphene oxide were introduced, dispersed nanoparticles with different sizes and shapes were deposited on the supports, which led to variously enhanced hydrogen production activities. The relationships between the morphologies of the Fe/H2 N-MCM-41 or Fe/graphene composites generated in situ and the hydrogen production activities were investigated systematically.