Surface capacitive charge storage in carbon nanodots-anchored hybrid halide perovskites

Surface faradaic process can bring about storage (pseudocapacitive) mechanism that store much more energy than conventional electric double-layer capacitors (ELDCs) quite rapidly. Many transition metal oxides possess pseudocapacitor properties, but only few are capable of providing a high power capability because of their low intrinsic conductivities. Here we demonstrate that lead- and bismuth-based hybrid halide perovskites, anchored with carbon nanodots, can operate at rates exceeding those of ELDCs and provide higher area normalized and volumetric capacitances than standalone halide perovskites and carbon dots. We report carbon nanodots in methyl ammonium bismuth iodide (CNDs/MBI) and methyl ammonium lead iodide (CNDs/MPI) hybrid electrodes, designed to facilitate electron transfer and cation accessibility to faradaic active sites. Devices based on CNDs/MBI and CNDs/MPI electrodes are able delivered up to 550 Fg⁻¹ and 402 Fg^-1, with corresponding energy densities of 76.5 Wh/kg and 55.8 Wh/kg at scan rates of 0.01 V⁻¹. Deconvolution of the cyclic voltanogramm also provide insight to fraction of charge storage due to surface- and diffusion-controlled process.