Integrated Photoelectrode and Electrolyte Engineering via Carbon Quantum Dots for Self-Powered H₂O/O₂-Mediated...

We developed N-doped carbon quantum dots (N-CQDs) as both photocathode modifiers and electrolytes for self-powered portable photoelectrochemical (PEC) cells to generate electricity under visible-light illumination. Using betaine-type Meldonium precursor, and either ethylenediamine, N,N-dimethylformamide or NH₃·H₂O as a nitrogen source deliver three different N-CQDs featuring both surface-negatively-charged and positively-charged groups. Due to structural-directing template functionality of ethylenediamine, N-CQDs(en) incorporates the highest pyridinic-N content, which facilitates the charge conductivity and fine-regulates the reaction selectivity within Csp²-frameworks. As semiconductor-coatings electrodeposited on Cu₂O, N-CQDs(en) integrate with Cu₂O into heterojunctions (N-CQDs(en)/Cu₂O) to improve charge separation and promote 4e^- oxygen-reduction into water. Importantly, encapsulating an aqueous solution containing N-CQDs(en) in a gelatin/sodium L-pyroglutamate-derived conductor gives a quasi-solid-state electrolyte that facilitates the charge migration, improving the electrodes-electrolytes interfacial incompatibility, while also possibly helping to in situ complement active sites on the modified photocathode. Coupled with a FeNiOOH/FeN-decorated BiVO₄ photoanode, enabling the efficient 4e^- water oxidation, the complete system establishes a self-sustaining H₂O-O₂-H₂O cycle. The resulting PEC cell shows impressive electricity output for over 120 h under irradiation, enough to power some small electronics. Unlike conventional photovoltaics, this cell is moisture-tolerant, oxidation-resistant and concurrently harnesses light and chemical energy, presenting a new paradigm for next-generation light-to-electricity conversion.