Microfabricated Pseudocapacitors Using Ni(OH)2 Electrodes Exhibit Remarkable Volumetric Capacitance and Energy Density

Metal hydroxide based microfabricated pseudocapacitors with impressive volumetric stack capacitance and energy density are demonstrated. A combination of top‐down photolithographic process and bottom‐up chemical synthesis is employed to fabricate the micro‐pseudocapacitors (μ‐pseudocapacitors). The resulting Ni(OH) 2 ‐based devices show several excellent characteristics including high‐rate redox activity up to 500 V s –1 and an areal cell capacitance of 16 mF cm –2 corresponding to a volumetric stack capacitance of 325 F cm –3 . This volumetric capacitance is two‐fold higher than carbon and metal oxide based μ‐supercapacitors with interdigitated electrode architecture. Furthermore, these μ‐pseudocapacitors show a maximum energy density of 21 mWh cm –3 , which is superior to the Li‐based thin film batteries. The heterogeneous growth of Ni(OH) 2 over the Ni surface during the chemical bath deposition is found to be the key parameter in the formation of uniform monolithic Ni(OH) 2 mesoporous nanosheets with vertical orientation, responsible for the remarkable properties of the fabricated devices. Additionally, functional tandem configurations of the μ‐pseudocapacitors are shown to be capable of powering a light‐emitting diode.