ABSTRACT
BiVO4-based photoanode is one of the most promising photoanodes for photoelectrocatalytic water splitting. However, the serious problem of interface charge recombination limits its further development. Here, a Mo:BiVO4/NiOx/CPF-TCzB/NiCoBi photoanode is constructed with double hole transport layer and an energy level gradient to achieve an effective photo-generated holes extraction and accumulation at the surface electrocatalyst. The conjugated polycarbazole framework CPF-TCzB is used as hole transport layer to eliminate the charge recombination center between Mo:BiVO4 and NiCoBi electrocatalyst and realize the extraction and storage of photo-generated hole; NiOx nanoparticles are further inserted between Mo:BiVO4 and CPF-TCzB to form a gradient energy level, eliminating the energy level barrier and optimizing band alignment. As a result, Mo:BiVO4/NiOx/CPF-TCzB/NiCoBi achieves a much higher photocurrent densities of 3.14 mA cm-2 than that of Mo:BiVO4 (0.42 mA cm-2) at 0.6 V versus RHE. This work provides an specific way to adjust the band structure of BiVO4-based photoanodes and realize efficient hole extraction and storage for PEC water splitting.
ABSTRACT
Alkaline zinc-based flow batteries (AZFBs) have emerged as a promising electrochemical energy storage technology owing to Zn abundance, high safety, and low cost. However, zinc dendrite growth and the formation of dead zinc greatly impede the development of AZFBs. Herein, a dual-function electrolyte additive strategy is proposed to regulate zinc nucleation and mitigate the hydroxide corrosion of zinc depositions for stable AZFBs. This strategy, as exemplified by urea, introduces an electrolyte additive to coordinate with Zn2+/Zn with proper strength, slowing zinc deposition kinetics to induce uniform nucleation and protecting the deposited zinc surface from attack by hydroxide ions through preferable adsorption. The zincate complexes with urea are identified to be Zn(OH)2(urea)(H2O)2 and Zn2(OH)4(H2O)4(urea), which exhibit slow zinc deposition kinetics, allowing instantaneous nucleation. Calculation results reveal an additional energy barrier of 1.29 eV for the subsequent adsorption of an OH- group when a urea molecule absorbs on the zinc cluster, significantly mitigating the formation of dead zinc. Consequently, prolonged cell cycling of the prototype alkaline zinc-iron flow battery demonstrates stable operation for over 130 h and an average coulombic efficiency of 98.5%. It is anticipated that this electrolyte additive strategy will pave the way for developing highly stable AZFBs.
