| Overuse of fossil fuel will aggrevate the problems of environmental pollution and gloable warming.Thus,the development of a clean,renewable energy as a substitute for fossil energy is a matter of utmost urgency.Among many alternative energy strategies,hydrogen energy with the highest energy density per unit mass and pollution-free production,may enable an effective,secure and clean energy future.Among the various methods for hydrogen production,water electrolysis is considered as a pormising strategy due to its aboundant and easy availability of raw materials and its independence of fossil fuel.Fuel cell is a device that converts chemical energy into electric energy directly,which has attracted worldwide attention for its high efficiency and environmental protection.In the catalytic electrode materials,the catalysts based on precious materials such as Pt and etc.are limited in their application by the high cost,limited reserves,easily poisoned and deactivated in the electrolytes.Therefore,it is of great significance to develop non-precious metal catalysts with high performance and low cost in this area.Firstly,bimetallic Co Fe-glycerate hollow sphere?Co Fe G-HS?with richness of oxyhydroxides has been synthesized successfully by one-pot method.Applied for anodic reaction in water electrolysis?OER?,Co Fe G-HS shows more excellent OER performance than commercial Ru O2 catalyst,due to the fact that overpotential at 10 m A·cm-2 of 242m V and Tafel slope of 49.4 m V·dec-1 for Co Fe G-HS,lower than 319 m V and 111.0m V·dec-1 for Ru O2,respectively.According to the time-dependent experiments,the growth process of Co Fe G-HS is in line with Ostwald-ripening mechanism.With the comparison of catalysts after annealing,the fresh catalysts exhibit highly activie performance,which is attributed to richness of oxyhydroxides playing an important role in the OER process.Higher OER performance of Co Fe G-HS than Co-glycerate and Fe-glycerate indicates the specific hollow structure and synergistic effect between Co and Fe ions could facilitate catalytic OER process.Secondly,bimetallic?Fe and Mn?analogous MOF-74 precursor were synthesized successfully by solvothermal method.After mixed with melamine and annealed at 800oC in N2 atmosphere,a core-shell catalyst could be obtained with structure of nitrogen doped carbon nanotubes encapsulate Fe-Mn alloy nanoparticles.When applied for cathodic reaction in fuel cell?ORR?,Fe3Mn1/N-CNTs-100 exhibits the best ORR activity and stability.Its half-wave potential of 0.865 V is higher of 10 m V than that of commercial Pt/C catalysts.After chronoamperometry test for 10000 seconds,Fe3Mn1/N-CNTs-100 maintains a high relative current of 96.1%,while Pt/C maintains only 60%.The excellent ORR performance could benefit by the combination between two kinds of active sites pyridinic N species and Fe2N species,larger specific area,appropriate pore size and unique microstructure protecting active sites.Based on the experiments in acid and alkaline electrolyte,it could be found that Fe2N species could catalyze ORR in both acid and alkaline solution,while the pyridinic N species could only facilitate ORR in the alkaline electrolyte. |
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