Beta-phased Ni(OH)2nanowall film with reversible capacitance higher than theoretical Faradic capacitanceElectronic supplementary information (ESI) available: detailed experimental procedure, specific capacitance estimation, SEM images. Discharge curves on control samples. See DOI: 10.1039/c1cc13796d

β-Ni(OH)2was constructed into a three-dimensional mesoporous film on Ni foam with ultra-thin (∼6 nm) primary nanowalls showing ultrahigh specific capacitance (2675 F g−1) and excellent cycling performance (>96% for 500 cycles). The capacitance was higher than theoretical value possibly due to the combination of Faradic and electrical double-layer capacitances. [ABSTRACT FROM AUTHOR]