Exploring the effect of graphite-coating on hexanary high entropy metal oxides towards efficient water electrocatalysis

High-entropy oxides (HEOs) have emerged as promising electrocatalysts due to their high configurational entropy, modular electronic structures, and defect-rich multicationic lattices. However, modifying their electrochemical kinetics through conductive surface modification remains completely unknown. An Al-rich hexanary spinel, Cr, Cd, Fe, Mg, and Mn-based materials were synthesized using a sol-gel method and then modified with graphite (5–20 wt%) via rotary ball milling to improve conductivity and interfacial charge transfer, resulting in a stable spinel phase as validated by Rietveld-refined XRD. The addition of graphite significantly increased anodic activity, with the 10 wt% composite (HEO-10C) achieving a peak current density of 47.09 mA cm−2 in 1 M KOH + methanol. This was followed by decreased charge-transfer resistance and better electron-transfer kinetics. The graphite-HEO interface allows for faster reaction pathways, as evidenced by a high diffusion coefficient (8.65 × 10−8 cm2 s−1), a heterogeneous electron-transfer rate constant (3.75 × 10−4 cm s−1), and a low Tafel slope of 97 mV dec−1. To better measure intrinsic activity, we add a new descriptor, Jη = (Jₚ (peak current density)−Jₒₙₛₑₜ (onset current density)), which represents the net operating current above onset. Jη correlates strongly with traditional kinetic measurements, highlighting the conductivity-driven performance gain in HEO-10C (44.59 mA cm−2), which is about 1.6× greater than the uncoated HEO. These findings confirm graphite coating as a viable method for modifying multication HEO electrodynamics and introduce a new measure for assessing advanced oxide-based electrocatalysts.