Incorporation of Ion Transport Chains into Multivariate MOF for Improved Water Oxidation

The climate crisis demands clean energy technologies to cut CO₂ emissions from fossil fuels. Hydrogen fuel cells and solar-driven CO₂ reduction are promising, but both rely on efficient water oxidation. Polypyridyl ruthenium complexes are active catalysts for water oxidation; however, they exhibit poor stability and recyclability. Our group improved performance by embedding these complexes into metal-organic frameworks (MOFs). As water oxidation is pH-dependent, proton management further enhances reactivity. To address the issue, we introduced proton transfer pathways into the MOF structure. Specifically, we incorporated -SO₃H groups onto the biphenyl linkers of UiO-67 loaded with [Ru-(tpy)-(dcbpy)-OH₂]-PF₆ catalyst (where tpy = 2,2':6',2″-terpyridine; dcbpy = 5,5-dicarboxy-2,2'-bipyridine). The sulfonated MOF exhibited a 2.5-fold increase in oxygen evolution compared to the nonsulfonated analogue. After 1 h of electrolysis, the sulfonated MOF exhibited a turnover number of 25 for oxygen evolution reaction compared to 10 for the native MOF, demonstrating the benefits of built-in proton management.