High-entropy layered oxide electrocatalyst derived from spent battery cathodes for overall water splitting and 2,5 hydroxymethylfurfural (HMF) oxidation

Abstract

The rapid expansion of lithium-ion battery (LIB) use has led to a critical waste management challenge, with end-of-life cells contributing to environmental degradation and resource depletion. Here, we report a low-temperature (100 °C) synthesis of high-entropy layered oxides, Li_xNa_1−x(NiCoMnFe)O₂, directly upcycled from spent LIB cathodes. These materials were designed and optimized as trifunctional electrocatalysts for overall water splitting (HER and OER) and 5-hydroxymethylfurfural (HMF) oxidation. Systematic compositional tuning revealed that the Ni-rich variant outperforms its counterparts, achieving overpotentials of 434 mV for the HER and 310 mV for the OER at 10 mA cm⁻², with corresponding Tafel slopes of 113 and 81 mV dec⁻¹, approaching the performance of Pt/C and RuO₂ benchmarks, respectively. Simultaneously, this catalyst facilitates the selective electrooxidation of HMF to 2,5-furandicarboxylic acid (FDCA), achieving an FE of about 18% for FDCA and around 64% for hydrogen during co-electrolysis. The catalyst retains activity over 16 h during flow-cell operation. A cradle-to-gate life-cycle assessment shows that allocating environmental impacts to FDCA as a co-product reduces impacts relative to a hydrogen-only pathway. Moreover, as the electricity source is the dominant source of CO₂ footprint, switching to renewable grids can lower the global warming potential (GWP, in Kg CO₂-eq) by ≈80%. Our work offers a scalable, energy-efficient platform that integrates LIB waste remediation with renewable hydrogen generation and biomass upgrading.