ZIF-67 Derived Nanostructures of Co/CoO and Co@N-doped Graphitic Carbon as Counter Electrode for Highly Efficient Dye-sensitized Solar Cells

In this work, a facile one-step approach is reported for using ZIF-67 as a sacrificial template in the synthesis of a counter electrode (CE) catalyst for dye-sensitized solar cells (DSCs). Porous nanocomposites of Co, CoO and N-doped graphitic carbon were synthesized by controlling the carbonization temperature of the templates in a N2 atmosphere. The characterization of the structure of the products indicated that cobalt nanoparticles were embedded in an N-doped graphitic carbon matrix, (a core-shell structure termed Co@NGC) while cobalt and cobalt oxide nanoparticles were exposed on the external surface of the carbon (termed Co/CoO). In particular, the chemical stability of the nanostructure of the Co@NGC was superior to Co/CoO with respect to etching by strong acids such as hydrochloric acid (HCl, 0.1 M). The DSC performance of ZIF-67-850 (pyrolyzed at 850 °C) employed as a CE resulted in a photoelectric conversion efficiency (PCE) of 7.92%, which was close to a Pt CE (8.18%) in the liquid I3−/I− redox couple electrolyte. The excellent performance of ZIF-67-850 can be attributed to the synergetic effects between the Co and CoO coupled with the nitrogen doped graphitic carbon. The cost-effective porous Co/CoO and Co@NGC nanocomposites exhibit great potential for application as high performance CE in solar cells.