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.