Developing positively surface-charged carbon dots as “semiconductor electrolyte” for photo-electrochemical H2O2 production based on oxygen reduction

Abstract

Electrolyte modulation for tailoring photoelectrochemical (PEC) activity and selectivity is highly effective but has proved challenging. The major obstacle is lack of a universal strategy that aims for improving the system charge separation based on electrolyte optimization. Herein, we presented an idea as “semiconductor electrolyte”, which was developed from the imidazole chloride delivered carbon dot (CDs), and featured for the positive surface charge. The CDs aqueous solution can accumulate H2O2 on a CuBi2O4 photocathode via PEC O2 reduction reaction (ORR) at neutral pH without any traditional electrolyte. Combined with experimental measurements and theoretical calculation, the mechanism of system and function of CDs was characterized. As electrolytes, CDs solution enabled to tune the energy band location of CuBi2O4. The electrostatic interaction between positively-charged CDs and negatively-charged photocathode triggered the fast charge and mass migration during PEC proceeding. As semiconductors, CDs can fabricate a dynamic p-n heterojunction with CuBi2O4. These advantages facilitated the photo-induced charge separation, which contributed to the boosted photocurrent and improved stability in PEC system. As ORR occurred interface that incorporated active sites, CDs provided a hydrophilic and adjusted-electronic surface, which fascinated to confine O2 and reduced the kinetic barrier for H2O2 generation. As a result, H2O2 generation was regulated with 0.44 mM and faraday efficiency over 84 % within 10 min, nearly 3 times to the commonly-used Na2SO4 solution. Our work therefore provides a striking and facile strategy to tailor PEC activity and selectivity in a durable and robust pathway. Importantly, it will evoke to develop a universal protocol for regulating PEC performance by electrolyte modulation.