Structural Regulation Of Copper-and Carbon-based Catalysts And Their Electrocatalytic Reduction Of CO₂ Performance

The recent development of electrochemical reduction of CO₂ technology has opened up new possibilities of using CO₂ as a carbon raw material for commercial chemicals and fuels.Considering the ultimate goal of this technology is to achieve industrial production,we should take the low costs of the electrocatalysts used for electrochemical reduction of CO₂ into first consideration.Cu-and carbon-based electrocatalysts are widely sought after for their low cost.Cu-based electrocatalysts are one of the few metal catalysts that can convert CO₂ directly into high value-added hydrocarbons.In addition,carbon-based electrocatalysts with high specific surface areas are easy to use in practical application,becoming research hotspots gradually.However,the relatively low catalytic activity and poor catalytic stability of these two types of electrocatalysts are still difficult to overcome.Therefore,in the current research,it is essential to design and optimize the Cu-based and carbon-based electrocatalysts with high performance and stability for electrochemical reduction of CO₂.In this paper,Cu-based bimetallic catalysts are constructed to enhance the selectivity of CO₂ reduction products through the synergistic effect between bimetals and the growth direction of the catalysts crystal facets;Cu-based metal oxidation derivatives are constructed to enhance the electrocatalytic activity and catalytic stability through the synergistic effect between Cu₂O QDs and HKUST-1;heteroatom-doped carbon-based electrocatalysts are constructed to significantly enhance the activity of non-doped carbon-based electrocatalysts for the electrochemical reduction of CO₂.The main contents of this paper are as follows:1.Preparation of Cu-based bimetallic nanoparticles and their performance in electrochemical CO₂ reduction(1)We report the heterostructured bimetallic Cu-Sn-X NPs electrocatalysts(X represents the ratio of Cu Cl₂·2H₂O/Sn Cl₂·2H₂O)to electrochemical CO₂ reduction to HCOOH with high FE_HCOOH of 94.1%.Impressively,an appreciable selectivity for HCOOH is achieved on Cu-Sn-1 NPs in a significantly wider potential window of 400m V.The origin of enhanced activity in the wide negative potential range can be attributed to the appearance of abundant Cu/Sn interfaces after optimizing the ratio of Cu and Sn.We use experiments and characterizations to demonstrate the synergistic effect between the interfaces of Cu and Sn rendering the high selectivity for CO₂ to HCOOH in the wide negative potential range.(2)We have successfully prepared a series of bimetallic In-Cu NPs electrocatalysts using the in-situ growth method.We firstly convert the main production of electrochemical CO₂ reduction from a mixture of CO and HCOOH to approximately onefold HCOOH by changing the In/Cu ratio in the electrocatalysts structure to adjust the growth direction of the electrocatalysts crystal facets.In_1.5Cu_0.5 NPs electrocatalyst preferentially grows along the In(101)crystal plane when the molar ratio of In and Cu is 1.5:0.5.In electrochemical analysis,only the In(101)surface of In_1.5Cu_0.5 NPs is beneficial to the formation of HCOOH.We extend the GIXRD analysis and DFT calculations to analyze the detail orientations difference of a series of the In_xCu_y NPs crystal facets and the reasons for their high selectivity for the electrochemical reduction of CO₂.2.Preparation of Cu₂O QDs@HKUST-1 electrocatalysts and their performance in electrochemical CO₂ reductionWe have prepared Cu₂O NPs in a controlled manner using a multi-step Ostwald method.The reconstructed HKUST-1 coated Cu₂O QDs electrocatalysts were fabricated by hydrothermal method and incomplete etching of the Cu₂O NPs using the acidity of organic ligands.The reconstructed electrocatalysts have high specific surface areas,which allows strong adsorption of CO₂.On this basis,its special structure is used to facilitate the mass transfer process of CO₂.And Cu₂O QDs@HKUST-1 are rich in Cu₂O QDs active sites and can achieve high electrocatalytic activity.These properties culminate in the high-performance electrochemical reduction of CO₂ to C₂H₄ by Cu₂O QDs@HKUST-1 with up to FE_C2H4 51%and stability for more than 30 h.3.Preparation of heteroatom-doped carbon-based electrocatalysts and their performance in electrochemical CO₂ reduction(1)We mix HKUST-1 and dicyandiamide as precursors,and successfully constructed a Cu and N co-doped carbon-based electrocatalysts using high-temperature annealing method.By tuning the annealing temperature and the applied potential of Cu-N-C electrodes,we were able to easily tune the H₂/CO ratio in the clean syngas products in a large range with high FE(?100%).Specifically,the Cu-N sites in Cu-N-C are seen as the active sites,and the high specific surface area of the carbon material matrix provides more Cu-N sites and excellent electronic conductivity.Therefore,the interactions between Cu,N and C can modulate the catalytic activity of the electrocatalyst and then improve mass transfer and charge transfer,which enables Cu-N-C catalyst has high selectivity,stability and catalytic activity for electrochemical CO₂RR.(2)We use the second-calcined ug-C₃N₄ and glucose as the precursor,and successfully prepare high-activity UNCNs electrocatalysts using the high-temperature calcination method.Impressively,by tuning the applied potential of the UNCNs-900electrode,we can easily tune the H₂/CO ratios in clean syngas within a wide range with extra high FE(?100%).And the maximum FE_CO could reach 91%which represents the highest values among the reported non-metallic carbon-based electrocatalysts for CO₂ reduction to syngas.According to the results of experiments and DFT calculations,we have proved that pyridinic-N in UNCNs-900 is the active site of CO₂RR,and graphitic-N may be the active site for HER.