Coralloid Co2P2O7 Nanocrystals Encapsulated by Thin Carbon Shells for Enhanced Electrochemical Water Oxidation
Yingxue Chang, Nai-En Shi,[2,3] Shulin Zhao, Dongdong Xu, Chunyan Liu, Yu-Jia Tang,  Zhihui Dai, Ya-Qian Lan, Min Han,[1, 3],*(韩敏) and Jianchun Bao,*(包建春)
 Jiangsu Key Laboratory of Biofunctional Materials, School of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210023, P. R. China
 State Key Laboratory of Coordination Chemistry, Nanjing National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, P. R. China
ACS Appl. Mater. Interfaces, Aug. 2016, 8(34),22534-22544.
Core-shell nanohybrids containing cheap inorganic nanocrystals and nanocarbon shells are promising electrocatalysts for water splitting or other renewable energy options. Despite great progress has been achieved, biomimetic synthesis of metal phosphates@ nanocarbon core-shell nanohybrids remains a challenge, and their use for electrocatalytic oxygen evolution reaction (OER) has not been explored. In this paper, novel nanohybrids composed of coralloid Co2P2O7 nanocrystal cores and thin porous nanocarbon shells are synthesized by combination of the structural merits of supramolecular polymer gels and controllable thermal conversion technique, i.e., temperature programmable annealing of pre-synthesized supra- molecular polymer gels that containing cobalt salt and phytic acid under proper gas atmosphere. Electrocatalytic tests in alkaline solution show that such nanohybrids exhibit greatly enhanced electrocatalytic OER performance compared with that of Co2P2O7 nanostructure. At a current density of 10 mA cm-2, their overpotential is 0.397 V, which is much lower than Co2P2O7 nanostructures, amorphous Co-Pi nanomaterials, Co(PO3)2 nanosheets, Pt/C, and reported some OER catalysts, and close to commercial IrO2. Most importantly, both of their current density at the overpotential over 0.40 V and durability are superior to IrO2 catalyst. As revealed by a series of spectroscopic and electrochemical analysis, their enhanced electrocatalytic performance results from the presence of thin porous nanocarbon shells, which not only improve interfacial electron penetration or transfer dynamics but also vary coordination environment and increase the number of active 5-coordinated Co2+ sites in Co2P2O7 cores.