Beta-phased Ni(OH)2 nanowall film with reversible capacitance higher than theoretical Faradic capacitance

β-Ni(OH)(2) was 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.