Local charge distribution manipulation by oxyhydroxide heterojunction toward urea photoelectrolysis

Photoelectrochemical urea splitting can simultaneously produce hydrogen and remediate urea wastewater, which can also reduce the need for the electric energy consumption of urea electrolysis. However, the lack of an appropriate cocatalyst severely restricts the improvement of photoelectrochemical activity for urea splitting. Here, we synthesize Co/Ni oxyhydroxide cocatalysts with a heterojunction configuration on the surface of BiVO4 films. Due to the difference in Fermi energies, CoOOH and NiOOH catalysts serve as nucleophilic and electrophilic active sites, respectively. Thus, the carbonyl group and amino group of urea can adsorb on CoOOH and NiOOH through the bridging coordination, respectively. Meanwhile, the charge transfer across CoOOH/NiOOH heterointerface improves the oxidation state of Ni species in NiOOH. The heterojunction cocatalyst and high oxidation state of Ni species promote the adsorption and fracture of chemical groups in urea molecules. Thanks to the composite design of photoanode, under AM1.5G illumination, the composite photoanode exhibits a photocurrent density of 4.93 mA/cm2 at 1.23 VRHE under neutral conditions, which is the highest value achieved with BiVO4. The onset potential of the composite photoanode shifts negatively by 140 mV. This work demonstrates that the fabrication of heterojunction cocatalysts is an effective strategy toward urea photoelectrolysis. [Display omitted] •Co/Ni oxyhydroxide heterojunction cocatalyst is synthesized via electrodeposition.•CoOOH and NiOOH serve as nucleophilic and electrophilic active sites, respectively.•High oxidation state of Ni(4+δ)+ generates with the assistance of photogenerated holes.•CoOOH/NiOOH/BiVO4 achieves a photocurrent density of 4.93 mA/cm2 at 1.23 VRHE.