Enhanced photoelectrocatalytic oxidation of hypophosphite and simultaneous recovery of metallic nickel via carbon aerogel cathode

Carbon aerogel (CA) cathode was adopted to an undivided-chamber photoelectrocatalytic system with TiO2 nanotube arrays (TNA) photoanode to enhance the oxidation of hypophosphite (H2PO2−) and simultaneous recovery of metallic nickel (Ni). Both the efficiencies of H2PO2− oxidation and Ni recovery were significantly enhanced after replacing Ti or carbon fiber paper cathode with CA cathode. With 1.0 mM H2PO2− and 1.0 mM Ni2+, the ratio of PO43− production increased from ∼41% or ∼54% to ∼100%, and the ratio of Ni recovery increased from ∼20% or ∼ 37% to ∼93% within 180 min at 3.0 V. H2PO2− was finally oxidized to PO43− by •OH radicals, which was speculated to be generated from UV/H2O2 and bound on TNA photoanode. Meanwhile, Ni2+ was eventually electro-reduced to metallic Ni by a two-electron reduction reaction. The efficiencies of H2PO2− oxidation and Ni recovery were favored at higher cell voltage, faintly acid conditions and larger H2PO2− concentration. The stability of this system exhibited that the ratio of PO43− production increased significantly in each cycle, which was attributed to the increase of H2O2 in-situ-generation via CA cathode caused by deposition of metallic Ni. Finally, the treatment of actual electroless nickel plating effluents was demonstrated. [Display omitted] •H2PO2− oxidation and Ni recovery were largely enhanced via carbon aerogel cathode.•The pathways of H2PO2− oxidation by •OH radicals and Ni2+ deposition were proposed.•Oxidation of H2PO2− and cathodic deposition of metallic Ni were mutually promoted.•The treatment of actual electroless nickel plating effluents was demonstrated.