Enhanced borohydride oxidation kinetics with Au@MOF-808 nanocomposite electrocatalysts with ultra-low Au loading

The highly stable metal-organic framework (MOF) composed of [Zr 6 O 4 (μ 3 -OH) 4 (OH) 6 (H 2 O) 6 (BTC) 2 ]·nH 2 O units (MOF-808) was modified by incorporating gold (Au) nanoparticles and functional groups to enhance electrocatalytic activity for the borohydride oxidation reaction (BOR). Three composite materials (Au@MOF-808, Au@MOF-808-NH 2 , and Au@MOF-808-SH) were prepared by the incorporation of Au in structurally related MOFs, MOF-808, MOF-808-NH 2 , and MOF-808-SH, respectively. These composite materials were evaluated as anodic electrocatalysts for BOR in alkaline media using cyclic voltammetry and chronoamperometry. Among the prepared materials, Au@MOF-808-NH 2 exhibited the highest BOR activity, with an apparent activation energy of 15.3 kJ mol −1 , a reaction order of 0.6, an anodic charge transfer coefficient of 0.63, and a number of exchanged electrons of 4.4. The latter was significantly below the theoretical eight-electron value, indicating the presence of alternative reaction pathways. Notably, this material achieved a high mass-specific BOR peak current of 4.23 A μg Au −1 , demonstrating outstanding electrocatalytic efficiency despite the ultralow noble metal loading. These results underscore the potential of Au@MOF-808-NH 2 as a cost-effective and scalable anodic electrocatalyst for high-performance direct borohydride fuel cells. • Ultralow Au-loaded functionalized MOF-808 boosts borohydride oxidation reaction (BOR). • Au@MOF-808-NH 2 shows the highest BOR activity among the prepared composites. • Record-high mass activity of 4.23 A μg Au −1 achieved with Au@MOF-808-NH 2 electrocatalyst. • A low activation energy of 15.3 kJ mol −1 suggests an efficient BOR pathway. • BOR mechanism involves partial BH 4 − hydrolysis, as implied by a 4.4-electron transfer behaviour.