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To combat global warming and achieve carbon neutrality, researchers from The Hong Kong Polytechnic University (PolyU), led by Prof. Daniel LAU, Chair Professor of Nanomaterials and Head of the Department of Applied Physics, have unveiled a groundbreaking electroreduction system capable of converting carbon dioxide (CO2) into ethylene.
This achievement, recently published in Nature Energy and recognised with a Gold Medal at the 48th International Exhibition of Inventions Geneva in Switzerland, marks a pivotal development in the quest for sustainable industrial practices.
The urgency to address climate change stems from the escalating threat it poses to both human society and ecological systems, with carbon dioxide being a primary contributor to the greenhouse gases responsible for climate warming.
The researchers at PolyU have responded to this challenge with an innovative electrocatalytic CO2 reduction system, utilising green electricity to transform carbon dioxide into ethylene, a valuable chemical widely used in polymer manufacturing, including the production of plastics and chemical fibres.
Ethylene, represented chemically as C2H4, is a crucial chemical in various industries globally. Traditionally derived from petrochemical sources, its production process contributes significantly to carbon footprints. The PolyU research team’s breakthrough aims to provide a sustainable and environmentally friendly alternative, aligning with the imperative of reducing CO2 emissions.
The heart of the innovation lies in the APMA system, a term coined by the research team, where ‘A’ stands for anion-exchange membrane (AEM), ‘P’ represents the proton-exchange membrane (PEM), and ‘MA’ indicates the resulting membrane assembly. Prof. Lau’s ingenious approach involves dispensing with the alkali-metal electrolyte, instead using pure water as a metal-free anolyte. This strategic choice prevents the formation of carbonates and salt deposition, enhancing the stability of ethylene production.
Key to the success of the system is the alkali-metal-free cell stack containing the APMA and a copper electrocatalyst, which exhibited a high specificity of 50% in ethylene production. Impressively, the system operated for over 1,000 hours at an industrial-level current of 10A, a substantial increase in lifespan compared to existing systems, indicating its potential for scalability to industrial proportions.
The research team’s method also addresses challenges encountered by previous systems. Carbonate and salt formation are suppressed, eliminating the risk of CO2 and electrolyte loss. This is a critical improvement over systems using bipolar membranes, where electrolyte loss occurs due to the diffusion of alkali-metal ions from the anolyte. Additionally, the system minimises the formation of hydrogen in competition with ethylene, overcoming a drawback observed in earlier systems employing acidic cathode environments.
An essential aspect of the process is the specialised electrocatalyst employed. While copper is a widely used catalyst in the chemical industry, the research team’s choice of a specific copper catalyst with nano-scale spheres, richly textured surfaces, and unique structural features enhances the efficiency of the reaction. The defects in the copper structure create a favourable environment for the reaction to proceed, contributing to the overall success of the electroreduction system.
Prof. Lau envisions continuous improvement in product selectivity and seeks collaboration opportunities with industry partners. He emphasised that the APMA cell design signifies a transition to green production not only of ethylene but also of other valuable chemicals. This breakthrough holds promise for significant contributions to reducing carbon emissions and realising the goal of carbon neutrality.
The PolyU project was a collaborative effort involving researchers from esteemed institutions such as the University of Oxford, the National Synchrotron Radiation Research Centre of Taiwan, and Jiangsu University. The collaboration underscores the global nature of the challenge posed by climate change and the necessity for collaborative solutions to address it.
