Synthesis of CoNi bimetallic alloy nanoparticles wrapped in nitrogen-doped graphite-like carbon shells and their electrocatalytic activity when used in a counter electrode for dye-sensitized solar cells

Nanoparticles of the bimetallic alloy CoNi wrapped in nitrogen-doped graphite-like carbon shells and dispersed on nitrogen-doped graphite-like carbon sheets (CoxNi1−x@NC) were synthesized by calcining CoNi metal–organic frameworks that were prepared through a facile solvothermal reaction using various raw-material molar ratios Co:Ni and CoNi:ethylenedinitrilotetraacetic acid. After depositing CoxNi1−x@NC for use as a counter electrode film in dye-sensitized solar cells, it was found that the electrocatalytic activity of the CoxNi1−x@NC counter electrode towards triiodide reduction could be optimized by simply tuning the molar ratios (Co:Ni and CoNi:ethylenedinitrilotetraacetic acid) appropriately during CoxNi1−x@NC synthesis. Cells that utilized a CoxNi1−x@NC counter electrode exhibited strong chemical-composition-dependent photovoltaic performance. Under optimal conditions, the CoxNi1−x@NC counter electrode presented an impressive energy conversion efficiency of 3.58%, suggesting that it is a highly promising counter electrode for application in dye-sensitized solar cells. This counter electrode has the advantages that it is considerably less expensive than a Pt counter electrode and that it provides the basis for the design and preparation of other inexpensive and efficient counter electrodes to replace Pt.