MoP-protected Mo oxide nanotube arrays for long-term stable supercapacitors

•We overcome the poor stability of MoO3 electrodes in aqueous electrolytes for supercapacitors.•We thermally produce an amorphous MoP protective shell on Mo oxide nanotube arrays.•The result is a capacitance retention of ∼93% over 10,000 charging/discharging cycles.•The MoP-protected nanotube arrays can be used as binder-free electrodes.•The structures deliver a non-intercalation-based volumetric capacitance of over 2000 F cm−3.