PolyU develops high-efficiency carbon dioxide electroreduction system for reducing carbon footprint and progressing carbon neutrality goals
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THE SYSTEM DEVELOPED BY PROF. LAU AND HIS TEAM CAN ACCELERATE THE DEVELOPMENT OF CO2 ELECTROCATALYSIS TECHNOLOGY, POTENTIALLY REVOLUTIONISING MODERN FOSSIL FUEL ENERGY SYSTEMS.
view moreCREDIT: © 2024 RESEARCH AND INNOVATION OFFICE, THE HONG KONG POLYTECHNIC UNIVERSITY. ALL RIGHTS RESERVED.
Global warming continues to pose a threat to human society and the ecological systems, and carbon dioxide accounts for the largest proportion of the greenhouse gases that dominate climate warming. To combat climate change and move towards the goal of carbon neutrality, researchers from The Hong Kong Polytechnic University (PolyU) have developed a durable, highly selective and energy-efficient carbon dioxide (CO2) electroreduction system that can convert CO2 into ethylene for industrial purposes to provide an effective solution for reducing CO2 emissions. This research was recently published in Nature Energy and won a Gold Medal at the 48th International Exhibition of Inventions Geneva in Switzerland.
Ethylene (C2H4) is one of the most in-demand chemicals globally and is mainly used in the manufacture of polymers such as polyethylene, which, in turn, can be used to make plastics and chemical fibres commonly used in daily life. However, it is still mostly obtained from petrochemical sources and the production process involves the creation of a very significant carbon footprint.
Led by Prof. Daniel LAU, Chair Professor of Nanomaterials and Head of the Department of Applied Physics, the research team adopted the method of electrocatalytic CO2 reduction - using green electricity to convert carbon dioxide into ethylene, providing a more environmentally friendly alternative and stable ethylene production. The research team is working to promote this emerging technology to bring it closer to mass production, closing the carbon loop and ultimately achieving carbon neutrality.
Prof. Lau’s innovation is to dispense with the alkali-metal electrolyte and use pure water as a metal-free anolyte to prevent carbonate formation and salt deposition. The research team denotes their design the APMA system, where A stands for anion-exchange membrane (AEM), P represents the proton-exchange membrane (PEM), and MA indicates the resulting membrane assembly.
When an alkali-metal-free cell stack containing the APMA and a copper electrocatalyst was constructed, it produced ethylene with a high specificity of 50%. It was also able to operate for over 1,000 hours at an industrial-level current of 10A – a very significant increase in lifespan over existing systems, meaning the system can be easily expanded to an industrial scale.
Further tests showed that the formation of carbonates and salts was suppressed, while there was no loss of CO2 or electrolyte. This is crucial, as previous cells using bipolar membranes instead of APMA suffered from electrolyte loss due to the diffusion of alkali-metal ions from the anolyte. The formation of hydrogen in competition with ethylene, another problem affecting earlier systems that used acidic cathode environments, was also minimised.
Another key feature of the process is the specialised electrocatalyst. Copper is used to catalyse a wide range of reactions across the chemical industry. However, the specific catalyst used by the research team took advantage of some distinctive features. The millions of nano-scale copper spheres had richly textured surfaces, with steps, stacking faults and grain boundaries. These “defects” – relative to an ideal metal structure – provided a favourable environment for the reaction to proceed.
Prof. Lau said, “We will work on further improvements to enhance the product selectivity and seek for collaboration opportunities with the industry. It is clear that this APMA cell design underpins a transition to green production of ethylene and other valuable chemicals and can contribute to reducing carbon emissions and achieving the goal of carbon neutrality.”
This innovative PolyU project was a collaboration with researchers from the University of Oxford, the National Synchrotron Radiation Research Centre of Taiwan and Jiangsu University.
a,b, The BPM system (a) and reaction (b) with an acidic cathode environment in reverse bias mode. c,d, The APMA system (c) and reaction (d) with an alkaline cathode environment in forward bias mode. e,f, The commercial BPM system (e) and reaction (f) with a bipolar junction/bonding at the AEL/CEL interface in forward bias mode.
a, A scanning electron microscopy image of SS-Cu. b,c, Typical HRTEM images of SS-Cu, revealing abundant stacking faults (b) and grain boundaries (c) with inset atomic-resolution HAADF-STEM images from the area highlighted with a yellow rectangle. The yellow lines in the insets highlight stacking faults and five-fold twin boundaries. d, An atomic-resolution HAADF-STEM image showing stepped faces induced by a stacking fault and a twin boundary, both along {111} planes (dashed white lines). e, GPA strain (ε) mapping on d, showing tensile strain near the surface exits of the stacking fault and the twin boundary, using the lattice far from these defects as a reference (zero strain). The measured strain is perpendicular to the {111} plane along which the stacking fault and twin boundary align.
a,b, The FEs towards ECO2R products under a range of applied potentials under 1 M KOH (a) and 1 M H3PO4 containing 3 M KI as the catholyte and 1 M H3PO4 as the anolyte (b), respectively. c,d, The partial current densities of C2H4 under a range of applied potentials under 1 M KOH (c) and 1 M H3PO4 containing 3 M KI as the catholyte and 1 M H3PO4 as the anolyte (d), respectively. Values are means, and error bars indicate the s.d. (n = 3 replicates).
a, A schematic of the APMA-MEA system architecture for ECO2R. b, The resistance of the system at different reaction temperatures. c, The FEs of gas products and corresponding cell voltages of the system at a total current density of 300 mA cm−2 for different reaction temperatures. d, The anodic gas product analysis of the pure-H2O-fed APMA system at 60 °C with a total current density of 300 mA cm−2. Ti fibre felt sputtered with Pt (Pt/Ti) was used as the anode electrode, and the flow rate of the CO2 inlet was 30 sccm. e, In situ Raman spectra of ECO2R on SS-Cu in 0.1 M KOH, pure H2O and bare electrode after ~20 min. f, The mass spectra of ECO2R using H218O as the anolyte in the APMA system. g, The total overpotential of all the reactions at different reaction temperatures. Values are means, and error bars indicate the s.d. (n = 3 replicates), except for g, where the values are means and the error bars indicate the effect of the AEM’s pH on the overpotential (setting the pH of the AEM in the range of 8–14).
a, The FEs towards ECO2R products under a range of applied current densities, and the corresponding cell voltages without iR compensation. b, The FEs towards ECO2R products under a range of applied cell voltages without iR compensation, and the corresponding total current density. c,d, Comparisons of the FEs (c) and partial current densities (d) towards C2H4 in the pure-H2O-fed APMA-MEA and AEM-MEA systems with 1 M KOH as the anolyte. e, A schematic of the APMA-MEA cell stack containing six APMA-MEA cells for the ECO2R reaction. f, The system stability performance of ECO2R to C2H4 on SS-Cu in a pure-H2O-fed APMA-MEA cell stack containing six APMA-MEA cells at a constant current of 10 A. Each cathode electrode area was 30 cm2, and the reaction temperature was 60 °C. Pt/Ti was used as the anode electrode, and the flow rate of the CO2 inlet was 30 sccm for the single cell or cell stack. AEM and PEM membranes were used as the electrogenerated OH− and H+/H3O+ ion exchange membranes, respectively. Values are means, and error bars indicate the s.d. (n = 3 replicates).
CREDIT
© 2024 Research and Innovation Office, The Hong Kong Polytechnic University. All Rights Reserved.
JOURNAL
Nature Energy
METHOD OF RESEARCH
Experimental study
SUBJECT OF RESEARCH
People
ARTICLE TITLE
Pure-water-fed, electrocatalytic CO2 reduction to ethylene beyond 1,000 h stability at 10 A
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