纳米材料及其在电催化领域的研究进展

综述了纳米材料的小尺寸效应、体积效应、表面效应、量子尺寸效应等特性,并详细介绍了不同纳米催化材料的分类与制备方法。此外,进一步介绍了纳米电催化材料所具有的特殊性质,概述了近年来人们对纳米电催化剂的研究成果和其在电催化领域中的一些应用,并详细介绍了用于直接甲醇燃料电池中对甲醇催化氧化的纳米电催化剂的研究现状。对今后纳米电催化材料的研究方向进行了展望。

Realizing efficient electrochemical oxidation of 5-hydroxymethylfurfural on a freestanding Ni(OH)_(2)/nickel foam catalyst

With the continuous improvement of solar energy production capacity,how to effectively use the electricity generated by renewable solar energy for electrochemical conversion of biomass is a hot topic.Electrochemical conversion of 5-hydroxymethylfurfural(HMF)to biofuels and value-added oxygenated commodity chemicals provides a promising and alternative pathway to convert re-newable electricity into chemicals.Although nickel-based eletrocatalysts are well-known for HMF oxidation,their relatively low intrinsic activity,poor conductivity and stability still limit the poten-tial applications.Here,we report the fabrication of a freestanding nickel-based electrode,in which Ni(OH)_(2) species were in-situ constructed on Ni foam(NF)support using a facile ac-id-corrosion-induced strategy.The Ni(OH)2/NF electrocatalyst exhibits stable and efficient electro-chemical HMF oxidation into 2,5-furandicarboxylic acid(FDCA)with HMF conversion close to 100% with high Faraday efficiency.In-situ formation strategy results in a compact interface between Ni(OH)_(2) and NF,which contributes to good conductivity and stability during electrochemical reac-tions.The superior performance benefits from dynamic cyclic evolution of Ni(OH)_(2) to NiOOH,which acts as the reactive species for HMF oxidation to FDCA.A scaled-up device based on a continu-ous-flow electrolytic cell was also established,giving stable operation with a high FDCA production rate of 27 mg h^(-1)cm^(−2).This job offers a straightforward,economical,and scalable design strategy to design efficient and durable catalysts for electrochemical conversion of valuable chemicals.

Efficient photoelectrocatalytic CO_2 reduction by cobalt complexes at silicon electrode

Two homogeneous photoelectrocatalytic systems composed of simple polypyridyl Co complexes[Co(tpy)2](PF6)2and[Co(bpy)3](PF6)2as electrocatalysts and a Si wafer as the photoelectrode were used for combined photoelectrochemical reduction of CO2to CO.A high photocurrent density of1.4mA/cm2was observed for the system with the[Co(tpy)2](PF6)2catalyst and a photovoltage of400mV was generated.Faradaic efficiencies of CO were optimized to83%and94%for the[Co(tpy)2](PF6)2and[Co(bpy)3](PF6)2complexes,respectively,in acetonitrile solution with10%methanol(volume fraction,same below)as a protic additive.Addition of2%water volume fraction induced a large amount of non‐specific H2evolution by the Si photoelectrode.

3D hierarchically macro-/mesoporous graphene frameworks enriched with pyridinic-nitrogen-cobalt active sites as efficient reversible oxygen electrocatalysts for rechargeable zinc-air batteries

Efficient and affordable electrocatalysts for reversible oxygen reduction and oxygen evolution reactions(ORR and OER,respectively)are highly sought-after for use in rechargeable metal-air batteries.However,the construction of high-performance electrocatalysts that possess both largely accessible active sites and superior ORR/OER intrinsic activities is challenging.Herein,we report the design and successful preparation of a 3D hierarchically porous graphene framework with interconnected interlayer macropores and in-plane mesopores,enriched with pyridinic-nitrogen-cobalt(pyri-N-Co)active sites,namely,CoFe/3D-NLG.The pyri-N-Co bonding significantly accelerates sluggish oxygen electrocatalysis kinetics,in turn substantially improving the intrinsic ORR/OER activities per active site,while copious interlayer macropores and in-plane mesopores enable ultra-efficient mass transfer throughout the graphene architecture,thus ensuring sufficient exposure of accessible pyri-N-Co active sites to the reagents.Such a robust catalyst structure endows CoFe/3D-NLG with a remarkably enhanced reversible oxygen electrocatalysis performance,with the ORR half-wave potential identical to that of the benchmark Pt/C catalyst,and OER activity far surpassing that of the noble-metal-based RuO2 catalyst.Moreover,when employed as an air electrode for a rechargeable Zn-air battery,CoFe/3D-NLG manifests an exceedingly high open-circuit voltage(1.56 V),high peak power density(213 mW cm^(–2)),ultra-low charge/discharge voltage(0.63 V),and excellent charge/discharge cycling stability,outperforming state-of-the-art noble-metal electrocatalysts.

Catalytic conversion of CO_2 to value added fuels: Current status, challenges, and future directions

The electrochemical reduction of C02 into liquid fuels especially coupling with the intermittent renewable electricity offers a promising means of storing electricity in chemical form, which reduces the dependence on fossil fuels and mitigates the negative impact of anthropogenic C02 emissions on the planet. Although converting CO2 to fuels is not in itself a new concept, the field has not sub- stantially advanced in the last 30 years primarily because of the challenge of discovery of structural electrocatalysts and the development of membrane architectures for efficient collection of reactants and separation of products. This overview summarizes recent advances in catalytic conversion of CO2 and presents the challenges and future directions in producing value-added fuels.

Preparation and application of electro-catalytic material Fe_2O_3-ZnO/C

Electro-catalysts Fe203 compounded by ZnO were prepared by a sol-gel method, which were titled as Fe203-ZnO. Electro-catalysts Fe203-ZnO loading on the bamboo charcoal was titled as Fe203-ZnO/C. The catalytic materials were characterized by X-ray diffraction （XRD） and scanning electron microscope （SEM）. The obtained catalysts were assembled to three-dimensional electrodes to degradation of chlorinated organic in paper wastewater. And the performance tests show that three-dimensional electrodes have high activities for degradation of chlorinated organic in paper wastewater. There are many factors affecting the electro-catalytic performances of the three-dimensional electrodes. And the orthogonal experiment results show that the optimum operating condition is as follows： the calcination time of the catalysts 2 h, the mass ratio of Fe to Zn 4：1, the voltage 12 V, the mass of the catalytic materials 6 g, the value of pH 9, and the treating time 2.5 h. Under these conditions, the optimum removal efficiency of chlorinated organics in paper wastewater is 47.58%.

Taguchi-Optimized Catalytic Growth of Carbon Nanotubes for Applications in Electro-Catalysis

Taguchi method, largely used to optimize processes controlled by manifold parameters, has been utilized to improve the synthesis of carbon nanotubes by chemical vapor deposition of isobutane. Analyzing results obtained in nine suitably designed reactions, the influence of synthesis （773-973 K）, calcinations （723-1,023 K） and reduction （773-973 K） temperatures and catalyst-support （alumina, magnesia or Na＋-exchanged K10 clay） on specific yield and crystallization degree （i.e., C sp2 content） of the nanotubes has been ranked. After critical examination and adjusting of conditions predicted to give optimal results, -50 g of nanotubes per gram of metal are obtained at 973 K over Fe/alumina catalysts calcined at 723 K and reduced at 773 K. Under the same conditions, highly crystallized nanotubes （with 73% of C sp2 bonds, as qualitatively estimated from Raman spectroscopy）, suitable for electro-catalysis applications, are synthesized over Fe/clay catalysts.

Regulating the electronic structure of NiFe layered double hydroxide/reduced graphene oxide by Mn incorporation for high-efficiency oxygen evolution reaction

The development of highly efficient and costeffective oxygen evolution reaction(OER)electrocatalysts for renewable energy systems is vitally essential.Modulation of the electronic structure through heteroatom doping is considered as one of the most potential strategies to boost OER performances.Herein,a rational design of Mn-doped NiFe layered double hydroxide/reduced graphene oxide(Mn-NiFe LDH/rGO)is demonstrated by a facile hydrothermal approach,which exhibits outstanding OER activity and durability.Experimental results and density functional theory(DFT)calculations manifest that the introduction of Mn can reprogram the electronic structure of surface active sites and alter the intermediate adsorption energy,consequently reducing the potential limiting activation energy for OER.Specifically,the optimal Mn-NiFe LDH/rGO composite shows an enhanced OER performance with an ultralow overpotential of 240 mV@10 mA cm^(-2),Tafel slope of 40.0 mV dec^(-1) and excellent stability.Such superior OER activity is comparable to those of the recently reported state-of-the-art OER catalysts.This work presents an advanced strategy for designing electrocatalysts with high activity and low cost for energy conversion applications.

Synergistic trifunctional electrocatalysis of pyridinic nitrogen and single transition-metal atoms anchored on pyrazine-modified graphdiyne

Multifunctional catalysts that integrate high efficiency hydrogen evolution reaction(HER), oxygen evolution reaction(OER) and oxygen reduction reaction(ORR) catalytic activity in a single material are attractive for unitized regenerative fuel cells and overall water splitting technologies. As the best-known HER and ORR electrocatalysts, Pt and its alloys have only moderate OER activity. Ruthenium and iridium oxides exhibit the highest OER activities but not as active as Pt for HER and ORR. Here, we proposed a general principle for achieving trifunctional electrocatalysis for three reactions in a single material. Using the newly-synthesized pyrazine-modified graphdiyne(PR-GDY) as an example, we demonstrated that the synergistic effect of the pyridinic nitrogen and anchored transition-metal(TM) single atoms renders highly-efficient HER/OER/ORR trifunctional electrocatalytic activity. For the Ni-doped PR-GDY, the overpotentials for HER, OER and ORR can be respectively as low as -0.05, 0.29 and 0.38 V, which are comparable or even superior to the best-known single-functional and bi-functional precious electrocatalysts.These computational results offer not only a promising trifunctional electrocatalyst but also a strategy for the design of multifunctional electrocatalysts.

Bimetallic oxide coupled with B-doped graphene as highly efficient electrocatalyst for oxygen evolution reaction

Developing electrocatalysts with high performance and low cost for the oxygen evolution reaction(OER)is of great importance for fabricating renewable energy storage and conversion devices.Here,a series of boron-doped graphene(BG)-supported bimetallic oxides of Co and Ni were obtained and served as OER electrocatalysts.Surprisingly,the annealed Co-Ni-Ox/BG with a Co/Ni ratio of 1:1 exhibits high performance toward oxygen evolution in alkaline electrolyte.The overpotential is only 310 mV at the current density of 10 mA cm-2,superior to many mono-metallic oxides reported before,and even comparable to the commercial RuO2.The regulation of charge distribution in bimetallic oxides and the strong synergistic coupling effects together contribute to the superior electrocatalytic performance of the Co-Ni-Ox/BG toward OER.This study also offers several effective ways to design high-performance OER electrocatalysts for water splitting.

Surface-structure tailoring of ultrafine PtCu nanowires for enhanced electrooxidation of alcohols

Surface tailoring of Pt-based nanocatalysts is an effective pathway to promote their electrocatalytic performance and multifunctionality.Here,we report two kinds of one-dimensional(1D)ultrafine PtCu nanowires(smooth surface&rugged surface)synthesized via a wet chemical method and their distinct catalytic performances in electro-oxidation of alcohols.The alloyed PtCu nanowires having rough surfaces with atomic steps exhibit superior catalytic activity toward multiple electrochemical reactions compared with the smooth counterpart.Density functional theory simulations show the excellent reactivity of rugged PtCu na-nowires and attribute it to the surface synergetic Pt-Cu site which accounts for the promotion of water dissociation and the dehydrogenation of the carboxyl intermediate.The current study provides an insight into reasonable design of alloy nanocatalysts in energy-related electrocatalytic systems.

Greatly promoted oxygen reduction reaction activity of solid catalysts by regulating the stability of superoxide in metal-O_(2)batteries

Oxygen reduction reactions(ORRs)with one-or two-electron-transfer pathways are the essential process for aprotic metal-oxygen batteries,in which the stability of superoxide intermediates/products(O_(2)^(-),LiO_(2),NaO_(2),etc.)mainly dominates the ORR activity/stability and battery performance.However,little success in regulating the stability of the superoxides has been achieved due to their highly reactive characteristics.Herein,we identified and modulated the stability of superoxides by introducing anthraquinone derivatives as cocatalysts which functioned as superoxide trapper adsorbing the superoxides generated via surface-mediated ORR and then transferring them from the solid catalyst surface into electrolyte.Among the studied trappers,1,4-difluoroanthraquinone(DFAQ)with electron-withdrawing groups showed the highest adsorption towards superoxides and could efficiently stabilize LiO_(2)in electrolyte,which greatly promoted the surface-mediated ORR rate and stability.This highlighted the magnitude of adsorption between the trapper and LiO_(2)on the ORR activity/stability.Using an aprotic Li-O_(2)battery as a model metal-O_(2)battery,the overall performance of the cell with DFAQ was substantially improved in terms of cell capacity,rate capability and cyclic stability.These results represent a significant advance in the understanding of ORR mechanisms and promoting the performance of metal-O_(2)batteries.