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 TiO nanotube arrays (TNA) photoanode to enhance the oxidation of hypophosphite (HPO) and simultaneous recovery of metallic nickel (Ni). Both the efficiencies of HPO oxidation and Ni recovery were significantly enhanced after replacing Ti or carbon fiber paper cathode with CA cathode. With 1.0 mM HPO and 1.0 mM Ni, the ratio of PO 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. HPO was finally oxidized to PO by •OH radicals, which was speculated to be generated from UV/HO and bound on TNA photoanode. Meanwhile, Ni was eventually electro-reduced to metallic Ni by a two-electron reduction reaction. The efficiencies of HPO oxidation and Ni recovery were favored at higher cell voltage, faintly acid conditions and larger HPO concentration. The stability of this system exhibited that the ratio of PO production increased significantly in each cycle, which was attributed to the increase of HO in-situ-generation via CA cathode caused by deposition of metallic Ni. Finally, the treatment of actual electroless nickel plating effluents was demonstrated.