Tracking Mechanistic Pathway of Photocatalytic CO₂ Reaction at Ni Sites Using Operando, Time-Resolved Spectroscopy

Abstract

Harvesting solar energy for catalytic conversion of CO 2 into valuable chemical fuels/feedstocks is an attractive yet challenging strategy to realize a sustainable carbon-cycle utilization. Homogeneous catalysts typically exhibit higher activity and selectivity as compared with heterogeneous counterparts, benefiting from their atomically dispersed catalytic sites and versatile coordination structures. However, it is still a "black box" how the coordination and electronic structures of catalysts dynamically evolve during the reaction, forming the bottleneck for understanding their reaction pathways. Herein, we demonstrate to track the mechanistic pathway of photocatalytic CO 2 reduction using a terpyridine nickel(II) complex as a catalyst model. Integrated with a typical homogeneous photosensitizer, the catalytic system offers a high selectivity of 99% for CO 2 -to-CO conversion with turnover number and turnover frequency as high as 2.36 × 10 7 and 385.6 s −1 , respectively. We employ operando and time-resolved X-ray absorption spectroscopy, in combination with other in situ spectroscopic techniques and theoretical computations, to track the intermediate species of Ni catalyst in the photocatalytic CO 2 reduction reaction for the first time. Taken together with the charge dynamics resolved by optical transient absorption spectroscopy, the investigation elucidates the full mechanistic reaction pathway including some key factors that have been often overlooked. This work opens the "black box" for CO 2 reduction in the system of homogeneous catalysts and provides key information for developing efficient catalysts toward artificial photosynthesis.

Unique S-scheme heterojunctions in self-assembled TiO2/CsPbBr3 hybrids for CO2 photoreduction

“…To determine the origin of CO 2 photoreduction products, we performed an isotope-labeled carbon dioxide ( 13 CO 2 ) photocatalytic reduction over TC2. Since the amount of products without photosensitizer and hole sacrificial agent was beyond the detection limit of mass spectrometry detector, we added tris(2,2’-bipyridyl)ruthenium(II) chloride hexahydrate ([Ru II (bpy) 3 ]Cl 2 ·6H 2 O) 36 and 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH) 37 into the system to promote the photocatalytic activity, which behaved as the photosensitizer and hole sacrificial agent, respectively. In this case, the production yields of H 2 and CO were significantly enhanced (Supplementary Fig.…”

A Ternary Dumbbell Structure with Spatially Separated Catalytic Sites for Photocatalytic Overall Water Splitting

“…The global energy demand continues to rise, which presents inextricably serious challenges to environment issues, and drives the quest for clean and renewable energy sources alternative to fossil fuels. [ 1–3 ] It has been regarded as a simple and cost‐effective method to produce clean hydrogen fuel by photocatalytic overall water splitting, [ 4–6 ] comparable to fossil‐fuel‐derived hydrogen due to its simplicity and low cost. [ 7–9 ] However, the photocatalysts for water splitting in previously reported literature still face grand challenges: 1) most of photocatalysts suffer from weak visible light response owing to their large bandgap; [ 10–12 ] 2) O 2 evolution from semiconductor photocatalysts is difficult due to multiple electrons and protons transfer process for the formation of OO bond (1.23 eV).…”

Inside‐and‐Out Semiconductor Engineering for CO2 Photoreduction: From Recent Advances to New Trends

“…Homogeneous and heterogeneous catalysis are two main branches of the catalysis family, both of which are applied in photocatalytic CO 2 conversion to produce hydrocarbons. Several advantages of homogeneous photocatalysts are depending on their atomically dispersed active sites, [ 428–430 ] tunable light absorption, [ 431–433 ] as well as high activity and selectivity. [ 434–439 ] Heterogeneous photocatalysts with relatively low cost are easy to synthesize and facile to be extracted and recycled for long‐term run.…”