Combination of ZIF-67 derived hollow porous Co9S8 nanocages and MWCNTs for electrochemical hydrogen storage applications

By using zeolitic imidazolate framework of ZIF-67 as the precursor, the hollow porous Co9S8 (H–Co9S8) nanocages are synthesized via the sulfidation reaction and thermal treatment processes. The ordinary solid Co9S8 (S–Co9S8) particles are prepared by hydrothermal method. To improve the conductivity and activity of the Co9S8 materials, H–Co9S8 + MWCNTs and S–Co9S8 + MWCNTs composites are fabricated by ball milling. The electrochemical hydrogen storage properties of H–Co9S8 and H–Co9S8 + MWCNTs electrodes are tested via a three-electrode system for the first time. Ultimately, the H–Co9S8 nanocages with hollow porous structure show higher discharge capacity of 667.1 mAh/g than the S–Co9S8 particles. The electrochemical performance enhanced after doping with MWCNTs. H–Co9S8 + MWCNTs displays the highest discharge capacity of 683.5 mAh/g. Additionally, the preferable high-rate dischargeability, corrosion resistance, and improved kinetic properties are also achieved for H–Co9S8 + MWCNTs. H–Co9S8 with a unique hollow structure and large specific surface area can offer sufficient electrochemical active sites to anchor hydrogen, meanwhile, MWCNTs with excellent electrical conductivity can further provide fast channels for charge transfer and improve the electrocatalytic activity of Co9S8 electrode during the charging/discharging processes.