The project has focused on designing and investigating novel materials with controlled facets and surface chemistry to explore structure-performance relationships. Below is a summary of the main results achieved in each work package (WP):
WP1: Controlling the Orientation of 2D Ag Nanoprisms We identified the edge ribs of Ag quasi-2D nanoprisms as highly active sites for CO2 reduction to CO. By using a superstructure design strategy, we prepared self-assembled two-dimensional Ag nanoprisms that maximize the exposure of active edge ribs. This control allowed us to investigate the role of the edges independently from other sites. We found that the edge ribs exhibit an overpotential of 150 mV compared to 550 mV for the basal plane with (111) facets. The vertically stacked Ag nanoprisms allow exposure of over 95% of the edge sites, resulting in enhanced selectivity and activity towards CO production from CO2, with a Faradaic efficiency over 90% for 100 hours and a partial energy efficiency for CO production of 70.5%.
WP1: Design of Single Atom Catalysts Single atomic catalysts (SACs) have emerged as next-generation catalysts for improving performance while decreasing the use of metal elements. Guided by density functional theory (DFT) simulations, we designed and characterized NiNx sites supported on nitrogen-doped carbon nanosheets for the electrocatalytic conversion of CO2 to CO. We also prepared Fe-doped ZIF-8, which was converted to SACs with Fe single atoms supported on N-doped carbon nanosheets after pyrolysis. These Fe-SACs exhibited remarkable performance for the nitrate reduction reaction (NO3RR), with a maximum Faradaic efficiency of over 95% for NO3RR to NH3. Additionally, we developed Fe-MoS2 SACs for the electrocatalytic nitrate reduction reaction, achieving a maximum Faradaic efficiency of 98% for NO3RR to NH3.
WP2: Molecular Doping for Multicarbon Products We developed a method to control the surface oxidation state of bimetallic Ag-Cu electrodes using functionalization. This approach improved the reaction rates and Faradaic efficiency towards the production of C2+ products. When assembled in a membrane electrode assembly flow electrolyzer, the catalyst delivered a selectivity for C2+ products of 80 ± 1% and a total C2+ energy efficiency of 20.3%. We also investigated the use of aryldiazonium salts to functionalize copper catalysts, achieving a Faradaic efficiency for ethylene of 83% at a full cell potential of -3.55 V. The addition of a perfluorinated sulfonic acid ionomer increased the Faradaic efficiency for ethylene to 89±3%.
WP3: Supersaturation Strategy for C3 Products We explored a supersaturation strategy for the direct electroreduction of CO2 to C3 products on a CuAg alloy catalyst using a strongly carbonated electrolyte. This approach led to a record-high Faradaic efficiency for 2-propanol of 56.7% at a specific current density of 59 mA cm−2. Our investigations revealed that supersaturated conditions promote the formation of *CO species on the catalyst surface, while the CuAg alloy favors the formation of multicarbon products.
WP3: Hydrogel Buffering Layer We developed a cross-linked polyethyleneimine (PEI) superaerophobic hydrogel buffering layer to promote mass transfer of in-situ produced CO2 gas bubbles while maintaining a high local cathode pH. This layer achieved high CO2 single-pass utilization and conversion rates, outperforming the best-reported results.
WP4: Degradation Mechanisms in HOIPs We investigated the degradation mechanisms affecting hybrid organic-inorganic perovskites (HOIPs), examining the interplay between material properties, compositions, and environmental stressors. We proposed a novel degradation mechanism for mixed 2D+3D HOIPs based on phase segregation upon hydration.
Overall, the 2D-4-CO2 project has made substantial contributions to the field of CO2 electroconversion, paving the way for sustainable energy solutions and reducing greenhouse gas emissions. The project's achievements have not only advanced scientific knowledge but also have practical implications for industry and environmental sustainability. The project led to the publication 18 research articles, 4 patent submissions including PCT application. It has led to the creation of a startup company: E-ETHYLENE (e-ethylene.com) in 2023 after the ERC-POC project: HIPECO2. It involved 2 PhD student, 6 postdoctoral researchers, 1 PI and several collaborator in Europe and outside.
