Carbon nano-onions combined with methylene blue for simple assembly of organic cells and batteries

This study introduces a novel approach to organic electrochemical cells by combining carbon nano-onions (CNO) with methylene blue (MB), a common redox-active dye, to create entropic concentration cells. CNO particles were characterized and incorporated into a carboxymethylcellulose (CMC) matrix to form a flexible film. When this film was applied to cellulose paper and treated with MB solution, the water-soluble CMC was removed, creating a pure CNO film with enhanced graphitic exposure, as confirmed by XPS analysis showing increased π–π* transitions (from 4.22% to 19.36%). Two cell configurations were tested: one using indium tin oxide (ITO) glass as cathode current collector (Al-CNO|MBH2+ǁMB+|ITO) and another using stainless steel and aluminum (Fe-CNO|MBH2+ǁMB+|Al). Both configurations yielded approximately 800 mV potential, though the latter demonstrated significantly higher current density (800 μA vs. a few μA). These cells operate primarily through entropic effects driven by MB concentration gradients across the paper separator, representing a fundamentally different approach from conventional battery systems. Our findings demonstrate the potential of CNO-MB systems for developing low-cost, environmentally friendly energy storage solutions with promising applications in flow batteries and pseudocapacitors, particularly for applications requiring both high power and energy density without the need for scarce mineral resources.