Photoelectrocatalytic hydrolysis of ammonia borane (AB) is a promising technique for producing hydrogen gas (H 2 ) in the presence of an appropriate photocatalyst under light irradiation and bias. The application of cuprous oxide on titanium dioxide nanotube arrays (Cu 2 O/TNA) for the photoelectrocatalytic hydrolysis of AB was studied. Cu 2 O/TNA exhibited a spectral response in the ultraviolet–visible region and an onset wavelength of 600 nm. With AB in an electrolyte, Cu 2 O/TNA exhibited a significant increase in its photocurrent spectral response at a bias of 0.1 V versus Ag/AgCl. The H 2 generation rate by photoelectrocatalysis (under 5-mW cm −2 irradiation at 455 nm; bias of 0.1 V vs . Ag/AgCl) was 0.018 μmol s −1 cm −2 , which was twice that by photocatalysis and four times those by catalysis and electrocatalysis; a Faradaic efficiency of 77% (corresponding to the oxidation reaction of AB) was also observed. Hence, Cu 2 O/TNA is an efficient photoanode for photoelectrocatalytic hydrolysis of AB. • Cu 2 O/TNA is a promising photoanode for photoelectrocatalytic hydrolysis of AB. • Cu 2 O/TNA performed a significant spectral response at 0.1 V versus Ag/AgCl. • H 2 generation rate by PEC was twice that by PC and four times those by C and EC. • The reaction at 0.1 V versus Ag/AgCl corresponded to the oxidation reaction of AB.