Researchers have developed highly efficient electrochemical systems that convert acetylene, a troublesome impurity and alternative feedstock, directly into high-purity ethylene, the world’s most produced organic compound. The new methods operate at ampere-level electrical currents, a critical threshold for industrial viability, and under ambient conditions, offering a cleaner and potentially more economical path for producing the foundational chemical of the global plastics industry. This advance points toward a future where renewable electricity powers the synthesis of essential chemicals, reducing reliance on fossil fuels and high-temperature industrial processes.
Ethylene is the primary building block for polyethylene, one of the world’s most common plastics, as well as numerous other chemical products. It is typically produced by the steam cracking of petroleum hydrocarbons, a process that invariably creates small amounts of acetylene as a highly undesirable byproduct. For decades, the industry has relied on energy-intensive thermocatalytic processes to either remove the acetylene or convert it. The newly demonstrated technologies achieve this conversion through electrocatalytic semi-hydrogenation (EASH), using water as the source of hydrogen and electricity as the engine. By successfully operating at industrial-scale current densities, these breakthroughs could lead to decentralized, electrically driven chemical plants that can purify ethylene streams or produce ethylene directly from non-petroleum sources.
Overcoming a Mass-Transport Bottleneck
One of the primary challenges in scaling up electrochemical conversion has been the physical movement of reactants and products within the electrode itself. A team led by researchers at the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences addressed this mesoscopic challenge by focusing on the physical arrangement of catalyst particles on the electrode surface. Their work, published in Angewandte Chemie International Edition, details how optimizing the space between catalyst particles can dramatically improve reaction efficiency.
Spacing Nanocubes for Better Flow
The DICP team worked with copper cube-shaped nanocrystals as the catalyst. They discovered that the performance of the electrocatalytic acetylene semi-hydrogenation was not solely dependent on the atomic-scale properties of the catalyst but was critically influenced by the average distance between the cubes. By increasing the average interparticle distance to 265 nanometers, they facilitated the transport of acetylene gas to the catalyst surface and the escape of the newly formed ethylene product. This improved spacing prevents the chemical equivalent of a traffic jam, allowing the reaction to proceed smoothly even at high rates.
Record Efficiency at High Currents
This structural optimization allowed the researchers to achieve an ethylene Faradaic efficiency of 97.4% while operating at a current density of 1.0 ampere per square centimeter (A/cm²). Faradaic efficiency is a measure of how effectively the electrons supplied are used to create the desired product. Furthermore, they recorded a maximum ethylene partial current density of 1.5 A/cm², one of the highest ever reported for this reaction. Finite element simulations and advanced spectroscopy confirmed that the wider spacing enhanced mass transport, which in turn accelerated the crucial steps of acetylene adsorption and ethylene desorption. Professor Gao Dunfeng of DICP noted that the study demonstrates the key role of mesoscopic mass transport in electrocatalysis, opening a new avenue for designing highly efficient industrial electrochemical systems.
A Tandem System for Unprecedented Purity
In a separate but related advancement, a team of researchers from Nanchang University and the University of Technology Sydney developed a novel tandem electrocatalytic system that achieves a near-total conversion of acetylene into ethylene. Described in the journal Advanced Materials, their system cleverly integrates an acetylene electrolyzer with a zinc-acetylene battery, creating a device that not only purifies the gas stream but also generates power.
Defective Nanoribbons as the Catalyst
The core of this technology is a unique catalyst made of ultrathin copper oxide (CuO) nanoribbons. Crucially, these nanoribbons were synthesized with a high concentration of oxygen vacancies—points in the crystal structure where an oxygen atom is missing. These vacancies proved to be the key to the catalyst’s high performance. According to experimental data and theoretical calculations, the oxygen vacancies make the catalyst exceptionally good at splitting water molecules to produce the active hydrogen atoms needed for the reaction. At the same time, they inhibit the over-hydrogenation of ethylene into ethane, ensuring the final product is the one desired.
Near-Perfect Conversion and Selectivity
When integrated into the tandem system, the catalyst performed with remarkable effectiveness. The device delivered a single-pass acetylene conversion of 99.998% at a high current of 1.4 amperes. This means that virtually every acetylene molecule passing through the reactor was converted. The selectivity for ethylene was 96.1%, an exceptionally high figure indicating that very few unwanted byproducts were formed. In the electrolyzer portion of the unit, the catalyst achieved an ethylene Faradaic efficiency of 93.2% at a current density of 1.0 A/cm².
A Greener Future for Chemical Production
Both research efforts represent a significant step toward replacing heat- and fossil-fuel-intensive processes in the chemical industry with cleaner, electricity-driven alternatives. The ability to use water as a hydrogen source under ambient temperature and pressure avoids the carbon emissions and high energy costs associated with traditional thermocatalytic methods, which use hydrogen gas produced from fossil fuels. By operating at ampere-level currents, these electrochemical systems prove they can handle the high reaction rates required for industrial production.
A techno-economic analysis performed as part of the tandem system research revealed that this new approach can dramatically reduce the overall cost of ethylene production compared to conventional processes. The establishment of a non-petroleum route for ethylene, whether for purification or direct synthesis from feedstocks like coal-derived acetylene, aligns with global efforts to decarbonize heavy industry and create more sustainable supply chains for essential materials. These advances lay the groundwork for a new generation of chemical reactors powered by renewable energy sources like solar and wind.
