Bimetallic MOF-derived CuO-Co3O4 heterostructures as high-capacity electrodes for asymmetric supercapacitors

Metal-organic frameworks (MOFs) offer unique opportunities for designing high-performance supercapacitor electrodes through controlled structural evolution. However, achieving optimal balance between conductivity, redox activity, and stability in MOF-derived oxides remains challenging. Here, we report a controlled room-temperature synthesis strategy for bimetallic Cu-Co MOFs with varying morphologies and tuneable Cu²⁺/Co²⁺ ratios, which, upon annealing, resulted in mixed-phase CuO-Co<inf>3</inf>O<inf>4</inf> heterostructures with oxygen vacancy density directly correlated to cobalt content. The CuO-Co₃O₄ (1:1) hybrid exhibits exceptional specific capacitance (1564.4 F g⁻¹ at 1 A g⁻¹), outperforming its parent MOF (333.3 F g⁻¹) and monometallic oxides by >300 %, attributable to synergistic Cu⁺/Cu²⁺ and Co²⁺/Co³⁺ redox couples and vacancy-enhanced ion diffusion. The electrochemical and structural characteristics were also verified by spin-polarised density functional theory (DFT) calculations. An asymmetric supercapacitor pairing of this hybrid with activated carbon achieves an extended 1.5 V window, delivering 48.7 Wh kg⁻¹ energy density at a power density of 750 W kg⁻¹ while retaining 91.2 % capacitance over 10,000 cycles – surpassing other reported MOF-derived oxides. The CuO-Co<inf>3</inf>O<inf>4</inf> electrodes lead to a combined synergistic effect due to the modified electronic state, higher active sites and improved redox activity, producing high supercapacitive performances. Our work demonstrates how metal ratio tuning in bimetallic MOF precursors can engineer defect-rich oxides for durable high-energy storage.