Microdroplet photofuel cells to harvest high-density energy and dye degradation

In this study, a membraneless photofuel cell, namely, μ-DropFC, was designed and developed to harvest chemical and solar energies simultaneously. The prototypes can also perform environmental remediation to demonstrate their multitasking potential as a sustainable hybrid device in a single embodiment. A hydrogen peroxide (H₂O₂) microdroplet at optimal pH and salt loading was utilized as a fuel integrated with Al as an anode and zinc phthalocyanine (ZnPC)-coated Cu as a cathode. The presence of n-type semiconductor ZnPC in between the electrolyte and metal enabled the formation of a photo-active Schottky junction suitable for power generation under light. Concurrently, the oxidation and reduction of H₂O₂ on the electrodes helped in the conversion of chemical energy into the electrical one in the same membraneless setup. The suspension of Au nanoparticles (Au NPs) in the droplet helped in enhancing the overall power density under photonic illumination through the effects of localized surface plasmon resonance (LSPR). Furthermore, the presence of photo-active n-type CdS NPs enabled the catalytic photo-degradation of dyes under light in the same embodiment. A 40 μL μ-DropFC could show a significantly high open circuit potential of ∼0.58 V along with a power density of 0.72 mW cm^-2. Under the same condition, the integration of ten such μ-DropFCs could produce a power density of ∼7 mW cm^-2 at an efficiency of 3.4%, showing the potential of the prototype for a very large scale integration (VLSI). The μ-DropFC could also degrade ∼85% of an industrial pollutant, rhodamine 6G, in 1 h while generating a power density of ∼0.6 mW cm^-2. The performance parameters of μ-DropFCs were found to be either comparable or superior to the existing prototypes. In a way, the affordable, portable, membraneless, and high-performance μ-DropFC could harvest energy from multiple resources while engaging in environmental remediation.