Tuning the Reconstruction of Metal-Organic Frameworks during the Oxygen Evolution Reaction

Abstract

Recently, there has been growing interest in the conversion of metal-organic frameworks (MOFs) into metal-hydroxide catalysts for alkaline oxygen evolution reactions (OERs). While studies have shown that the initial OER performance of MOF-derived intermediates surpasses that of traditional metal-hydroxide catalysts, ongoing debates persist regarding these catalysts' durability and electrochemical stability. Moreover, the inevitable reorganization (aging) of MOF-derived catalysts from disordered to ordered phases, particularly those primarily composed of nickel oxyhydroxides, remains a topic of discussion. To address these issues, we propose a straightforward approach to mitigating MOF reconstruction and modulating aging in harsh alkaline environments by introducing additional organic carboxylate linkers into electrolytes. Specifically, we focus on two examples: Ni-BPDC-MOFs and NiFe-BPDC-MOFs, of formula [M2(OH)2BPDC] (M: Ni and Fe; BPDC = 4,4′-biphenyldicarboxylate). Experimental results indicate that alkaline electrolytes containing additional BPDC linkers exhibit enhanced OER activity and a prolonged electrochemical lifespan. Complemented by in situ Raman spectroscopy, our findings suggest that manipulating the coordination equilibrium of the organic linker involved in Ni-MOF formation (linker assembly) and reconstruction (linker leaching) leads to the formation of more disordered nickel oxyhydroxide phases as the active catalyst material, which shows enhanced OER performance.