Multifunctional Tandem Catalytic System For Driving CO₂ Conversion To High-Value Products

The electrocatalytic reduction reaction of carbon dioxide（CO₂RR）represents an effective approach for both CO₂ capture and the storage of intermittent renewable energy sources,such as solar and wind energy,offering promising prospects for future energy transition and environmental protection.During the reaction process,a variety of value-added chemicals and fuels can be obtained,including single-carbon（C1）products like carbon monoxide（CO）and methanol（CH₃OH）,as well as multi-carbon(C₂₊)products such as ethylene（C₂H₄）and ethanol（C₂H₅OH）,among which C₂₊products have attracted significant attention due to their high energy density and economic value.Among all the investigated CO₂RR catalysts,copper（Cu）-based catalysts have demonstrated great potential for effective C₂₊product formation owing to the appropriate binding energy of*CO intermediates at Cu sites.However,the pathway of CO₂ conversion to various products via proton-coupled electron transfer（PCET）processes is intricate,and the structure-performance relationship is delicate and fragile.Therefore,seeking further enhancement in the management of*CO intermediates to promote the continuous output of high-efficiency single/multiple carbon products is crucial for the industrialization of CO₂RR.In this context,we introduce the concept of tandem catalytic systems,assembling CO sources catalysts（such as Ag nanoparticles,Ni-SAC,Pr-SAA,etc.）with Cu-based modified substrates to form assemblies.By constructing nano-reaction models on Cu substrates or introducing heteroatoms to enhance the confinement of*CO intermediates,we facilitate the forward pathway of CO₂RR to C₂₊products.Subsequently,we explore the optimization of high-current reaction devices to improve stability and maintain high selectivity under high currents.The specific contributions of this study are summarized as follows:（1）We design a series of Ag@Cu₂O nano-reactors composed of Ag-nuclei and multi-layer-constrained Cu shells to investigate the influence of*CO intermediates under confinement conditions on CO₂RR.The optimized Ag@Cu₂O-2 nano-reactor exhibits 74%Faradaic efficiency in the C₂₊pathway and maintains stability for over 10hours at a bias current density of 100 m A cm^-2.Finite element methods identify that a certain volume of cavity in Ag@Cu₂O-x nano-reactors contributes to the retention of CO on-site,while multi-layer Cu species facilitate CO capture.Density functional theory（DFT）calculations suggest that the preferential formation of ethanol products may originate from the（100）/（111）interface of Cu layers.The in-depth exploration of multi-layer-constrained nano-tandem reactors provides structural models and Cu-based crystal planes（interfaces）guidance for efficient C₂₊product generation.（2）We advance the concept of incorporating boron elements（B）into Cu catalysts as additional adsorption sites for*CO intermediates to enhance the selectivity of desired C₂₊products.Moreover,by using nickel single-atom catalysts（Ni-SAC）as CO source components to increase local CO concentration and alleviate hydrogen evolution reactions,we synthesize a series of Cu B_x-Ni_ySAC tandem catalysts with different B contents.In neutral electrolytes,the Cu B₂-Ni_0.05SAC mixed catalyst produces ethylene at a bias current density exceeding 300 mA cm^-2,while the Cu B₅-Ni_0.2SAC produces ethanol at a bias current density exceeding 250 m A cm^-2.X-ray photoelectron spectroscopy（XPS）combined with inductively coupled plasma-mass spectrometry（ICP-MS）illustrates differences in the distribution of B on the surface and bulk of Cu-based catalysts;in-situ experiments and DFT calculations indicate that surface-bound boron units more effectively adsorb and convert CO,promoting ethylene production,while boron elements in Cu bulk affect charge transfer and lattice arrangement,facilitating ethanol generation.Element doping in Cu-based catalysts not only induces changes in charge and crystal phase arrangement at Cu sites but also serves as complementary catalytic sites for coupled reactions,providing new insights and theoretical significance for achieving high-efficiency single/multiple C₂₊products.（3）To simplify catalyst synthesis steps and reduce costs,we adopt a one-pot synthesis method to obtain a series of praseodymium-doped（Pr）Cu B_x catalysts in single-atom alloy configurations.Pr single-atom sites exhibit high catalytic activity for CO₂,promoting the generation of locally high concentrations of*CO intermediates.Combined with Cu B_x control of*CO subsequent C-C coupling,high-efficiency ethylene production is facilitated.In classic flow cells,the bias current density for ethylene production exceeds 600 mA cm^-2,with a single Faradaic efficiency exceeding60%.Finally,in a novel membrane electrode system with pure water supply（no alkali metal ions）,CO₂ reduction to ethylene is achieved by integrating anion exchange membranes and proton exchange membranes on the cathode and anode,respectively.This system effectively suppresses carbonate formation and prevents salt precipitation,enabling stable operation for over 50 hours at a total current density of 300 m A cm^-2,with no CO₂ or electrolyte loss.In summary,this study promotes the regulation of simplified*CO in CO₂RR reactions via heteroatom doping in Cu-based catalysts,guiding*CO coupling to desired multiple carbon products pathways,and combined with the formation of sophisticated tandem catalytic systems.Through the optimization of reaction device conditions,the issues of salt precipitation and C loss are addressed,enhancing the stability of reaction systems,and providing new insights and practical value for the industrialization of high-efficiency C₂₊product generation in CO₂RR.