Periodic Reporting for period 2 - COOLEFIN (Novel Dinuclear Late Transition Metal Catalysts for CO2/Olefin and CO2/Epoxide/Olefin Copolymerization)
Période du rapport: 2020-10-01 au 2021-09-30
While anthropogenic carbon dioxide (CO2) emissions present a daunting societal challenge with respect to climate change, concentrated CO2 sources also afford an attractive CO2-recycling opportunity. The electrochemical carbon dioxide reduction reaction (CO2RR) is a catalytic process by which CO2-recycling can be driven via renewably derived electricity, hence affording a pathway toward zero- or low-carbon chemical/fuel feedstocks. Among all the products that can be obtained from the CO2RR, this project was especially interested in the development of electrocatalysts for the production of ethylene.
Ethylene is a commodity chemical generated on a massive scale annually (~200 MT/yr globally) with a market value of approximately $250 billion dollar per year. Ethylene refinement from oil plays a major role in the business models of large oil and chemical companies such as Exxon and Dow, where it is a precursor for polymers synthesis and other important chemicals. Current methods for ethylene generation contribute to 0.6% of the annual global carbon dioxide (CO2) generation. Complementary methods for sustainable ethylene production, directly from CO2 as the sole carbon source, are appealing, especially when they benefit from the utilization of renewable electricity.
The development of catalytic materials for the efficient conversion of CO2 into ethylene from renewable energy presents an exciting opportunity, but also a challenge for the field of catalysis. CO2RR can facilitate the transformation of CO2 into a range of desirable carbon-containing products through the use of metallic electrodes and renewable electricity. However, the mechanistic landscape of CO2RR is complex and competing proton-coupled electron transfer (PCET) pathways can be operative; the control of product selectivity remains a central issue. To circumvent the use of expensive separation processes that will hamper the large-scale implementation of electrochemical CO2RR, approaches for the rational design of selective catalytic surfaces are needed.
To date, copper is the only known metal capable of producing ethylene, from CO2RR with decent selectivity. Bridging homogeneous molecular systems with heterogeneous copper surfaces is a promising approach for the development of new electrodes, combining the advantages of both approaches. The objective of the project is to develop hybrid copper electrodes consisting of molecular organic films and a planar copper electrode to target high selectivity for ethylene.
Ethylene is a commodity chemical generated on a massive scale annually (~200 MT/yr globally) with a market value of approximately $250 billion dollar per year. Ethylene refinement from oil plays a major role in the business models of large oil and chemical companies such as Exxon and Dow, where it is a precursor for polymers synthesis and other important chemicals. Current methods for ethylene generation contribute to 0.6% of the annual global carbon dioxide (CO2) generation. Complementary methods for sustainable ethylene production, directly from CO2 as the sole carbon source, are appealing, especially when they benefit from the utilization of renewable electricity.
The development of catalytic materials for the efficient conversion of CO2 into ethylene from renewable energy presents an exciting opportunity, but also a challenge for the field of catalysis. CO2RR can facilitate the transformation of CO2 into a range of desirable carbon-containing products through the use of metallic electrodes and renewable electricity. However, the mechanistic landscape of CO2RR is complex and competing proton-coupled electron transfer (PCET) pathways can be operative; the control of product selectivity remains a central issue. To circumvent the use of expensive separation processes that will hamper the large-scale implementation of electrochemical CO2RR, approaches for the rational design of selective catalytic surfaces are needed.
To date, copper is the only known metal capable of producing ethylene, from CO2RR with decent selectivity. Bridging homogeneous molecular systems with heterogeneous copper surfaces is a promising approach for the development of new electrodes, combining the advantages of both approaches. The objective of the project is to develop hybrid copper electrodes consisting of molecular organic films and a planar copper electrode to target high selectivity for ethylene.
Through this project, we discovered a remarkably convenient and inexpensive means by which copper electrodes are modified to promote the production of ethylene. Our approach uses specific organic additives that alter the chemical properties of the copper electrode by creating an organic film on it. The resulting organic/copper hybrid electrode generates ethylene with remarkably high selectivity and activities approaching the minimum threshold established for a successful industrial application.
In our first published work we report a novel and convenient method for nanostructuring copper electrodes using N,N′‐ethylene‐phenanthrolinium dibromide as molecular additive. Selectivities up to 70 % for C-C coupled products (ethylene, ethanol and propanol) are observed for more than 40 h without significant change in the surface morphology. Mechanistic studies reveal several roles for the organic additive, including: the formation of cube‐like nanostructures by corrosion of the copper surface, the stabilization of these nanostructures during electrocatalysis by formation of a protective organic layer, and the promotion of C-C products.
We have then reported a molecular tuning strategy that stabilizes intermediates for more selective CO2RR to ethylene. We found that the adhered molecules improve the stabilization of certain population of carbon monoxide intermediate thereby favouring further reduction to ethylene. As a result of this strategy, we reported the highest CO2RR to ethylene rate ever reported with selectivity of 72% at a partial current density of 230 mA/cm2. We also reported the most stable ethylene electrocatalyst with constant ethylene production for 190 hours.
In another study, we have reported an adlayer functionalization catalyst design: a catalyst/tetrahydro-phenanthrolinium/ionomer (CTPI) interface in which the catalytically active copper is functionalized using a similar phenanthrolinium-derived film and a perfluorocarbon-based polymeric ionomer. We found that this hierarchical adlayer augments both the local CO2 availability and the adsorption of the key reaction intermediate carbon monoxide on the catalyst surface. Using this CTPI catalyst, we achieved an ethylene selectivity of 66% at a partial current density of 208 mA/cm2 in a membrane-electrode assembly set-up.
To get closer to a potential industrial application of our device, we have recently reported a tandem electrolyzer which drastically reduces the energy input of the CO2RR. We developed an integrated electrochemical system that comprises a solid-oxide CO2-to-CO electrochemical cell (SOEC) and a CO-to-C2H4 MEA electrolyser. The MEA is equipped with a hierarchical catalyst composed of Cu, N-tolyl-tetrahydro-bipyridine, and a short-side-chain (SSC) ionomer. The MEA, as a result, delivered a C2H4 selectivity of 65% and an energy efficiency (EE) of 28% at a current density of 166 mA cm-2. In the integrated system, we achieved a peak C2H4 production rate of ~1.3 mmol per hour and a total energy requirement of ~120 GJ per tonne of ethylene, which represents a ~45% reduction in energy intensity compared to literature benchmarks.
We have also performed extended mechanistic studies of our approach to have a better understanding of the role of the organic film in altering the selectivity profile of the CO2RR. We have demonstrated how in situ coating of a silver electrode via electrodeposition of an organic film selectively inhibits proton versus CO2 mass transport, thereby affording extremely selective (>99%) electrochemical CO2-to-CO conversion.
In our first published work we report a novel and convenient method for nanostructuring copper electrodes using N,N′‐ethylene‐phenanthrolinium dibromide as molecular additive. Selectivities up to 70 % for C-C coupled products (ethylene, ethanol and propanol) are observed for more than 40 h without significant change in the surface morphology. Mechanistic studies reveal several roles for the organic additive, including: the formation of cube‐like nanostructures by corrosion of the copper surface, the stabilization of these nanostructures during electrocatalysis by formation of a protective organic layer, and the promotion of C-C products.
We have then reported a molecular tuning strategy that stabilizes intermediates for more selective CO2RR to ethylene. We found that the adhered molecules improve the stabilization of certain population of carbon monoxide intermediate thereby favouring further reduction to ethylene. As a result of this strategy, we reported the highest CO2RR to ethylene rate ever reported with selectivity of 72% at a partial current density of 230 mA/cm2. We also reported the most stable ethylene electrocatalyst with constant ethylene production for 190 hours.
In another study, we have reported an adlayer functionalization catalyst design: a catalyst/tetrahydro-phenanthrolinium/ionomer (CTPI) interface in which the catalytically active copper is functionalized using a similar phenanthrolinium-derived film and a perfluorocarbon-based polymeric ionomer. We found that this hierarchical adlayer augments both the local CO2 availability and the adsorption of the key reaction intermediate carbon monoxide on the catalyst surface. Using this CTPI catalyst, we achieved an ethylene selectivity of 66% at a partial current density of 208 mA/cm2 in a membrane-electrode assembly set-up.
To get closer to a potential industrial application of our device, we have recently reported a tandem electrolyzer which drastically reduces the energy input of the CO2RR. We developed an integrated electrochemical system that comprises a solid-oxide CO2-to-CO electrochemical cell (SOEC) and a CO-to-C2H4 MEA electrolyser. The MEA is equipped with a hierarchical catalyst composed of Cu, N-tolyl-tetrahydro-bipyridine, and a short-side-chain (SSC) ionomer. The MEA, as a result, delivered a C2H4 selectivity of 65% and an energy efficiency (EE) of 28% at a current density of 166 mA cm-2. In the integrated system, we achieved a peak C2H4 production rate of ~1.3 mmol per hour and a total energy requirement of ~120 GJ per tonne of ethylene, which represents a ~45% reduction in energy intensity compared to literature benchmarks.
We have also performed extended mechanistic studies of our approach to have a better understanding of the role of the organic film in altering the selectivity profile of the CO2RR. We have demonstrated how in situ coating of a silver electrode via electrodeposition of an organic film selectively inhibits proton versus CO2 mass transport, thereby affording extremely selective (>99%) electrochemical CO2-to-CO conversion.
A recent techno-economic analysis demonstrates that ethylene produced from the CO2RR can be competitive with current industrial processes at ethylene partial current densities higher than 450 mA/cm2, for selectivities approaching 80% and a catalyst lifetime above 1000 h. We are encouraged by recent results from this project that have demonstrated ethylene production at partial current densities as high as 520 mA/cm2 and ethylene selectivity of 65%. Under optimal conditions, our electrolyzer was stable for 190 h at an ethylene partial current density of 370 mA/cm2 with a selectivity of 62%. These values represent a record for the field and represent a step forward to an industrial implementation.
The results of the project represent an important milestone toward the industrial production of ethylene from the CO2RR. More data will be published in the coming year based on recent results obtained during the end of the project. We have data which demonstrate that our hybrid copper electrode, as opposed to any other electrocatalyst reported in the literature, can break the so called “scaling relationship” which usually dictate the selectivity profile of heterogeneous catalysts. This is a significant discovery which open a totally new dimension of research for the development of hybrid electrocatalyst with better selectivity, activity and stability.
The results of the project represent an important milestone toward the industrial production of ethylene from the CO2RR. More data will be published in the coming year based on recent results obtained during the end of the project. We have data which demonstrate that our hybrid copper electrode, as opposed to any other electrocatalyst reported in the literature, can break the so called “scaling relationship” which usually dictate the selectivity profile of heterogeneous catalysts. This is a significant discovery which open a totally new dimension of research for the development of hybrid electrocatalyst with better selectivity, activity and stability.