Synergizing Donor-Acceptor Ni-MOF with Lignin Proton Relay for Efficient and Selective CO₂-to-CO Photoreduction

Amidst the urgent global push for carbon neutrality, CO₂-to-CO photoreduction has emerged as a critical technology for closing the carbon cycle and converting renewable energy. In this work, a hybrid catalyst, denoted as C-HL-20%/Ni(TTA)bpe (TTA = 4,4',4″;-tricarboxy-triphenylamine, bpe = 4,4'-ethylenedipyridine), is constructed through the rational design of a composite system incorporating carboxylated lignin (C-HL) and a single-crystalline Ni-based metal-organic framework (Ni-MOF). The catalyst demonstrates impressive photocatalytic performance, achieving a CO production rate of 6516.4 µmol g^-1 h^-1 with 98.3% selectivity, which has reached the top level of the reported MOF-based photocatalysts. Under outdoor conditions, it also demonstrates a stable CO₂-to-CO conversion rate of 4282.5 µmol g^-1 h^-1. Experimental characterizations and theoretical calculations reveal that this high activity originates from donor-acceptor (D-A) artificial structure of the single-crystalline Ni-MOF and proton-coupled electron transfer (PCET) process. Modification with C-HL introduces enriched ─COOH groups, which form hydrogen bonds with the Ni(TTA)bpe framework. This not only consolidates the structure but also shortens the electron migration pathway, thereby achieving efficient and selective CO₂-to-CO photo-conversion. This study establishes a rational catalyst design strategy for sustainable CO₂ photoreduction, demonstrating a feasible pathway toward manageable carbon resource utilization.