Effect of Meso- and Micro-Porosity in Carbon Electrodes on Atomic Layer Deposition of Pseudocapacitive V₂O₅ for High Performance Supercapacitors

Atomic layer deposition (ALD) of vanadium oxide is a viable means to add pseudocapacitive layers to porous carbon electrodes. Two commercial activated carbon materials with different surface areas and pore structures were acid treated and coated by V₂O₅ ALD using vanadium triisopropoxide and water at 150 °C. The V₂O₅ ALD process was characterized at various temperatures to confirm saturated ALD growth conditions. Capacitance and electrochemical impedance analysis of subsequently constructed electrochemical capacitors (ECs) showed improved charge storage for the ALD coated electrodes, but the extent of improvement depended on initial pore structure. The ALD of V₂O₅ onto mesoporous carbon increased the capacitance by up to 46% after 75 ALD cycles and obtained a maximum pseudocapacitance of 540 F/g­(V₂O₅) after 25 ALD cycles, while maintaining low electrical resistance, high columbic efficiency, and a high cycle life. However, adding V₂O₅ ALD to microporous carbons with pore diameters of <11 Å showed far less improvement, likely due to “blocking off” of the micropores and reducing the accessible surface area. Results show that ALD is a viable means to construct high-performance supercapacitors from activated carbon which is the basis for commercial products, and a clear understanding of carbon electrode pore structure, layer conformality, and layer thickness are necessary to fully optimize performance