Structure Design And Counter Electrode Performance Of Cobalt Compounds And Their Graphene Composites

For more than two hundred years,fossil energy has greatly contributed to the development of human society,but its excessive exploitation and use have inevitably destroyed the green mountains on which human beings depend and caused serious environmental problems.At the same time,fossil energy is non-renewable energy,and will be exhausted one day.Therefore,it is urgent to develop renewable-clean energy and adjust the fossil energy-dominated energy structure to solve the current energy-environmental problems.Solar energy is inexhaustible,harmless,pollution-free,safe and reliable while satisfying sustainable development.It has become an important part of the new energy structure,thus a variety of photovoltaic-photothermal devices also came into being.Dye-sensitized solar cells(DSSCs)with high efficiency,rich raw materials and simple assembly processes have been a hot topic in the photovoltaic field.In traditional DSSCs,the cost of Ti O₂ nanocrystals and photosensitive dyes is very low,and the overall cost of the cells is mainly due to the expensive platinum(Pt)counter electrode(CE).In addition,although Pt has excellent performance,it is easy to be corroded in iodine-containing electrolyte,which limits the stability of the cells.Therefore,the development of stable and low-cost Pt-free CE is extremely important for the mass production and future commercial application of DSSCs.Transition metal compounds have been widely studied in CE owing to the low cost,wide source of raw materials,easy structure control and excellent electrochemical properties.At the same time,the modification of graphene,carbon nanotubes and other carbon materials has been proved to be effective in improving the catalytic performance,electrical properties and stability of the composites.This paper is to take this as the starting point,taking the structure design of transition metal compounds such as Cu O/Co₃O₄,Co-NC as the center,combining with the modifying of graphene,exploring the synthesis of low-cost and high-efficient CE,and studying the role of structure optimization in improving the performance and cycle stability of CE.The following is the specific research content of the paper:(1)To optimize the microstructure of transition metal oxide heterostructure,a simple hydrothermal process and element doping were conducted,which successfully transformed the solid Co₃O₄ microspheres into the core-shell Cu O/Co₃O₄ microspheres.Finally,the Cu O/Co₃O₄ heterogeneous structure was packaged in the high-conductive graphene oxide and the Cu O/Co₃O₄@GO interfacial structure was prepared.The results show that the interfacial structure constructed by core-shell heterogeneous microspheres and GO effectively increases the specific surface area of the composites(86.7 m²·g^-1),thus providing more active sites for the redox reaction of I₃^-/I^-pair and accelerating the redox process.At the same time,the encapsulation of GO further increases the conductivity and stability of the composites,and finally obtains power conversion efficiency of 8.34%,which surpasses Pt in efficiency and stability.The results provide an effective way to improve the performance of low-cost Pt-free counter electrode.(2)The dual-carbon confined Co-NC@rGO composites were synthesized with a simple"seeding"strategy,via anchoring the ultra-thin carbon layer-coated Prussian blue derivatives on the reduced graphene oxide.The obtained Co-NC@r GO-600 composites not only realized excellent power conversion efficiency(the highest PCE=8.82%),but also showed strong stability in the electrolyte.Further studies show that the r GO with large specific surface area effectively dispersed cobalt nanoparticles,thus providing more active sites for the reduction of I₃^-ions.At the same time,the electron bridge constructed by surrounded nanocarbon and r GO has successfully optimized the electron transmission path and greatly enhanced the conductivity of the catalyst.In addition,the uniform encapsulation of the dual carbon materials effectively avoided the direct contact of the cobalt-rich active center and the electrolyte,thus greatly improving the stability of the sample.The experiment not only expands the application of Prussian blue derivatives,but also provides a new path for designing the electrode materials with high efficiency and strong stability.