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.