Customizing Ferrocene Units into Atomically Precise Cu₁₁ Clusters for Boosting Oxygen Reduction to H₂O₂

Precisely integrating an organometallic compound into atomically defined copper clusters holds great promise for boosting catalytic performance and uncovering detailed structure-activity relationships. Herein, we report the first successful synthesis of atomically precise copper clusters (Cu₁₁-DPPF, DPPF = 1,1-bis(diphenylphosphino)ferrocene) carrying ferrocene units using DPPF and cyclohexanethiol as coligands through a straightforward, scalable, and versatile synthetic strategy, which is also applicable to synthesize its analogous Cu₁₁-DPPM (DPPM = bis(diphenylphosphino)methane) and Cu₁₁-DPPE (DPPE = 1,2-bis(diphenylphosphino)ethane) clusters. All three Cu₁₁ clusters exhibit a similar structural feature like a cloverleaf-like rotational assembly, comprising three fused butterfly-shaped Cu₅S₇P₂ subunits. Among them, Cu₁₁-DPPF exhibits superior catalytic performance in the two-electron oxygen reduction reaction (2e^- ORR), achieving H₂O₂ selectivity exceeding 97.5% within the whole potential range of 0.35 to 0.55 V versus the reversible hydrogen electrode (RHE), fully deserving to be called the optimal 2e^- ORR catalyst in the metal cluster community. DFT simulations, in conjunction with multiple characterization techniques such as operando infrared spectroscopy and X-ray absorption fine structure spectroscopy, reveal that the introduction of ferrocene units in Cu₁₁ clusters facilitates favorable electron redistribution, which optimizes the adsorption of OOH* in the rate-determining step, thereby promoting efficient conversion of OOH* to H₂O₂. The practical efficacy of Cu₁₁-DPPF is further demonstrated in Fenton-like reactions for hydroxyl radical-initiated pollutant degradation via in situ H₂O₂ generation. This work provides crucial insights into the design of atomically precise ferrocene-functionalized copper cluster hybrid catalysts and deepens our understanding of their structure-activity relationships in 2e^- ORR pathways for H₂O₂ production.