Highly Ethanol-Selective Electrocatalytic CO2 Reduction Enabled by Site-Specific Heteroatoms Doped Single Atom Catalysts Supported Cu Clusters

Project Information

SAC-Cu-CO2RR

Grant agreement ID: 101105092

DOI

10.3030/101105092

Project closed

EC signature date 14 March 2023

Start date 1 May 2023

End date 30 April 2025

Funded under

• Marie Skłodowska-Curie Actions (MSCA)

Total cost

No data

EU contribution

€ 230 774,40

Coordinated by

AARHUS UNIVERSITET
Denmark

Periodic Reporting for period 1 - SAC-Cu-CO2RR (Highly Ethanol-Selective Electrocatalytic CO2 Reduction Enabled by Site-Specific Heteroatoms Doped Single Atom Catalysts Supported Cu Clusters)

Reporting period: 2023-05-01 to 2025-04-30

Summary of the context and overall objectives of the project

The COP 28 UN Climate Change Conference in Dubai (2023) conducted the first “global stocktake” of the world’s efforts to address climate change under the Paris Agreement, consenting to hasten the transition from fossil fuels to renewable sources, such as wind and solar power. However, for air transportation, steel, and cement plants et al., adoption of new energy sources necessitates significant technological innovation and cannot be achieved in a short timeframe. To abate these most persistent emissions, electrochemical carbon dioxide reduction reaction (eCO2RR) coupled with renewable electricity, is an elegant technology by utilizing CO2 to produce an alternative energy medium for the current fossil fuel. In this way, we can achieve a net-zero pathway for hard-to-decarbonize sectors. Among all products in eCO2RR, multicarbon (C2+) products have received extensive attention because it can be directly used as fuel in internal combustion engines and industrial power generation. Copper (Cu) has been considered as the predominant electrocatalyst for C2 products via promoting C-C coupling, but with a poor selectivity towards C2+.
Therefore, the objective of this project is to design carbon-based single atom catalysts (SACs) supported Cu clusters architecture to let it serve as a high-efficient catalyst for achieving a high C2+ selectivity (> 75%) at a low overpotential. In this project, I prepared Ni-based SACs with high-density of Ni by a modified method. And then, I combined the Ni-based SACs with Cu nanoparticles. Benefiting from the synergistic effect of Ni SACs and Cu nanoparticles, the prepared Ni-SACs/Cu tested in an H-cell and flow cell achieved a faradaic efficiency of ~60% towards C2+ products.
During the process of completing this project, I have been thinking about a question: Although eCO2RR is advancing quickly, the laboratory-bench efforts have been achieved by utilizing ultrapure CO2 (99.999%) as feedstock gas. It overlooked the upstream CO2 capture from point source and enrichment processes that expends a major energy and cost, thus reducing the economic benefits for design a real-world eCO2RR system. The electrochemical conversion of CO2-captured solvents (HCO3−), into value-added chemicals can bypass energy-intensive CO2 regeneration.
Accordingly, I slightly adjusted the focus of my MSCA project. Following the completion of eCO2RR using Ni-SACs catalysts, I further employed these catalysts—with strategic modifications—for bicarbonate electrocatalysis, achieving excellent performance under high current densities. This approach enables the in-situ generated CO2 to be efficiently reduced into value-added products, thus achieving an integrated CO2 capture and conversion strategy
This work provides a straightforward method for the synthesis of hybrid catalysts, which exhibited a good catalytic performance towards eCO2RR and bicarbonate electrocatalysis. It will push catalyst engineering to the next level of development and eCO2RR technology closer to techno-economic profitability.

No website has been developed for the project.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Working Package 1 (WP1): Synthesis of Ni-SACs with a high metal content.

Activities: By modifying metal-organic frameworks (MOFs) using secondary carbon and nitrogen sources, the skeleton of MOFs was preserved in the high-temperature pyrolysis. After pyrolysis of modified MOFs, the N-C with porosity and large surface area was obtained (denoted as N-C-l). Afterwards, the high-density Ni SACs were synthesized by adsorbing Ni cations onto N-C-l as the substrate (denoted as h-Ni-SACs). Meanwhile, as a controller, a Ni-SACs was prepared using the N-C substrates without modification process.
Main achievements: The prepared N-C-l substrates with porosity and large surface area were obtained. The large surface area of N-C-l has a great promise in guaranteeing enough hosting space for the subsequent anchor of more Ni single atom sites. Meanwhile, the abundant porosity provides sufficient channels to transport reactive species to the active sites and expose more active sites for improving the activity and selectivity in electrocatalysis. The proportion of Ni loadings in h-Ni-SACs were determined through inductively coupled plasma optical emission spectrometry (ICP-OES). The Ni content of is 1.85 wt%. The Ni content of Ni-SACs is 2.00 wt%. Compared to the h-Ni-SACs, there are some nanoparticles in Ni-SACs, which further revealed that the large surface area of N-C-l could prevent Ni single sites from aggregation.

Working Package 2 (WP2): Synthesis of Cu/h-NiN4 catalyst.

Activities: Two kinds of Cu species were prepared in my project: Cu clusters (c-Cu) and commercial Cu nanoparticles (Cu NP). The c-Cu/h-NiN4 were prepared by mixing Cu salts and h-Ni-SACs in the solution. After stirring overnight, the precipitates were collected and pyrolyzed. Cu NP/h-NiN4 were prepared by the spray Cu NP and h-Ni-SACs onto the carbon paper layer by layer.
Main achievements: For c-Cu/h-NiN4, the contents of Cu were adjusted. For Cu NP/h-NiN4, the numbers of layers and positions of Cu NPs layers were controlled.

Working Package 3 (WP3): Characterization of the Cu/x-NiN4 catalyst.

Activities: The crystal structure of the as-prepared catalysts is going to be examined by PXRD analysis. The X-ray photoelectron spectrometer (XPS) will be used to investigate specific chemical components and valence states. Surface morphologies of the Cu/x-NiN4 catalyst will be characterized by field emission scanning electron microscopy (FE-SEM). To directly identify the Cu cluster and Ni single atom sites, the spherical aberration corrected transmission electron microscope (Cs-TEM) will be used. Meanwhile, the isolated Ni single metal sites co-existing with N at the atomic level will be identified using electron energy-loss spectroscopy (EELS). In addition, EELS mapping images can show the element distributions. To further identify the electronic structure and coordination environment, X-ray absorption near edge structure measurements will be performed.

Main achievements: All the characterizations mentioned were finished.

Working Package 4 (WP4): Optimization of the eCO2RR performance in H-cell and flow cell for realizing real-world application.

Activities: First, eCO2RR was investigated on different samples in a typical gas-tight H-cell. Afterwards, the optimized catalysts were tested in a flow cell under a large current density. More importantly, to achieve good catalytic performance using the relevant catalysts towards bicarbonate electrocatalysis, the flow cell configuration has been re-designed in my project to suppress competing hydrogen evolution reaction and obtain a large current density.

Main achievements: The optimized catalyst demonstrated good C2+ product selectivity with FEC2H4 exceeding 40% in an H-cell. Furthermore, the ow cell assembled with the optimized catalysts achieved a high FEC2H4 of 55% at −300 mA cm−2. More importantly, in bicarbonate electrocatalysis, the h-Ni-SACs showed FECO exceeding 90% in an H-cell, along with long-term stability. the modified ow cell assembled with h-Ni-SACs achieved a high FECO of over 80% from −20 to −200 mA cm−2, outperforming other counterparts and demonstrating strong potential for industrial applications.

Working Package 5 (WP5): Mechanistic study on optimized electrodes.

Activities: Theoretical calculation was carried out.

Main achievements: The results obtained from Theoretical calculation really match the experimental results.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Electrochemical CO2 reduction reaction (eCO2RR) using renewable electricity provides a sustainable route to produce carbon-based fuels, which can realize the utilization of emitted CO2 and store renewable energy in usable form. Although current significant progress, including the projects I have participated in, has been achieved in enhancing selectivity and efficiency of eCO2RR under the ideal lab condition, the critical challenge is that the lab-level achievements are not enough to address the practical CO2 emission. One of the existing bottlenecks is the high operation cost for eCO2RR industrialization, which is caused by the captured CO2 purification. Because the laboratory-bench efforts have been achieved by utilizing ultrapure CO2 (99.999%) as feedstock gas. In my MSCA project, I achieved good catalytic performance not only using pure CO2, but also directly utilizing captured-CO2 solvents to generate high-purity products, outperforming other counterparts and demonstrating strong potential for industrial applications. It will push eCO2RR technology closer to the techno-economic profitability.

The scheme of high-density Ni SAC preparation with modification