Incorporating transition metals (Ta/Co) into nitrogen-doped carbon as counter electrode catalysts for dye-sensitized solar cells

Carbon materials are potential electrode materials in new energy devices such as solar cells, fuel cells, Li-ion batteries, and supercapacitors, because of their distinct advantages including low cost, high surface area, and high electric conductivity. Nitrogen doping can effectively improve the performance of carbon electrode materials, and introducing transition metals into nitrogen-doped carbon is a promising strategy to develop high-performance electrode materials. In the present work, we successfully prepared two kinds of metal-incorporated nitrogen-doped carbon materials (CoNC and Ta/CoNC) by pyrolyzing a cobalt (II) imidazolate polymer followed by ion exchange. The as-prepared Ta/CoNC materials present a better graphite crystal phase and higher Brunauer-Emmett-Teller (BET) specific surface area (421.5 m2/g) than that of CoNC (354.7 m2/g). As counter electrode (CE) materials in I-mediated dye-sensitized solar cells (DSSCs), Ta/CoNC exhibits a superior catalytic activity and electrochemical stability than CoNC, resulting in a high power conversion efficiency (PCE) of 7.96%, which outperforms the level achieved using a Pt electrode (7.19%) in DSSCs. These Ta- and Co-incorporated nitrogen-doped carbon materials are expected to be used in extensive new energy applications, such as biomass, pollution control and hydrogen generation.