Joint project "Renewable fuels for electricity production"
Renewable fuels from solar energy have the potential to replace fossil fuels and create CO2-free alternatives. While sequestration and storage of CO2 is an economical and energetic drawback, it is an advantage to upgrade unavoidable CO2 to methane (CH4) via renewable Hydrogen (H2) and thus replace fossil CH4. If CH4 and H2 are produced with such quality and efficiency as addressed in this joint project, commercially available solid oxide fuel cells (SOFC) and proton exchange membrane fuel cells (PEM) will offer additional CO2 savings when converted into electricity and heat.
Project description (completed research project)
The Swiss government has signed the Paris Climate Agreement, which implies that various measures need to be implemented in order to reach the target of a 50% reduction in CO2 emissions in Switzerland by 2030 compared to the value for 1990. Production of cement in Switzerland accounts for about 2.5 million tonnes of CO2 emissions, which corresponds to roughly 7% of the country’s total annual CO2 emissions. The research project examined how this CO2 – mainly unavoidable geogenic CO2 from the lime stone – could be put to good use to create a new value chain via CO2 methanation and thus help to reduce the consumption and import of fossil fuels in Switzerland. With the power-to-gas technology, this CO2 along with regenerative hydrogen from solar-to-fuel technologies can be converted into renewable synthetic natural gas, fed into the existing natural gas grid and consumed from fuel cell technologies.
The declared aim of this joint project was the technical evaluation of a value chain to convert all of the 2.5 million tonnes of cementitious CO2 into CH4 in order to replace fossil CH4 imports and thus reduce the corresponding CO2 emissions. This is achieved by producing H2 through solar water splitting (PEC), which is subsequently converted via a sorption-based CO2 methanation. Both H2 and CH4 are utilised in SOFC and PEM fuel cell technologies.
The joint project comprises four innovative approaches in the fields of materials research and modelling to enable a CO2 saving value chain for energy production. More efficient, lifetime improving and more cost competitive technologies are being examined within this value chain with the aim of reducing and reusing CO2:
- A Cu2O based HIT tandem
PEC system demonstrated 8.8% solar-to-hydrogen efficiency, by far the most efficient unbiased tandem system on oxide materials only. 100-hour stability with less than 10% degradation from nanostructured radial p-n junction was established.
- A sorption-enhanced
CO2 methanation catalyst demonstrated a groundbreaking 100% CO2 to-CH4 conversion at stoichiometric conditions and 300°C and thus reached a new level of efficiency and sufficiency with respect to the cost-driving H2. Operation time of the catalyst concept is enhanced by 300% from an improved support-catalyst interaction.
- Novel simulation models are developed to reduce transport losses in gas diffusion layers (GDL) and to simulate coupled transport processes in
PEM fuel cells, such as transport of gas components, liquid water, heat and charge in GDLs. The simulation software is available for industry and research.
- A unique perovskite (La,Sr)Ti0.95Ni0.05O3-d anode material for combined heat and power SOFC technology provides an innovative and outstanding functionality: a catalytic and microstructural self-regeneration. After severe degradation, i.e. particle growth and poisoning from H2S, the material fully recovers after redox cycling and provides pristine, nanostructured Ni domains. It provides the same activity as common anode materials but with 90% less Ni.
As part of a technology assessment, a cost estimation has established for the cementitious CO2, factoring in nowadays mature and available technologies (PV|alkaline electrolysis AEL|CO2 methanation), that all of the 2.5 million tonnes of cementitious CO2 can be converted from Swiss resources to renewable methane. This methane would replace 33% of the fossil gas imports!
Taking into account the additional CO2 savings from the integration of more efficient fuel cells into the energy grid, a fuel cell dominated domestic heating sector would generate 50% CO2 savings compared to conventional systems. However, H2 production is by far the most expensive production step in the value chain and contributes to about 90%. Therefore, renewable methane currently costs three times more than fossil methane. To be more competitive, either PV and electrolysis must get cheaper or photo-electrochemical cells (PEC) must become less costly. The sorption-based CO2 methanation will create a substantial economic benefit, with an additional 25% efficiency as well as sufficiency for the H2.
- A Cu2O based HIT tandem
Implications for research
The scientific key findings are based on novel and innovative concepts which are groundbreaking for electrochemistry, catalysis and modelling in energy conversion research. Transferring and adopting these key findings to other research fields will enlighten and enrich those disciplines. The project has shown that catalytic systems can recover catalytic performance and their pristine, highly dispersed condition after severe degradation. Additionally, conversion rates of 100%, overcoming “thermodynamic limitations” by so-called sorption-enhanced CO2 methanation will push “Power to X” concepts towards new frontiers. A further scientific impact is generated by the transfer of the PEM fuel cell models on transport of gas, liquid water, heat and charge into water electrolysis, an important key technology in the future renewable energy system. PEC technology, not yet ready for commercialisation, has shown outstanding performance improvement, but the material stability in such a complex layered structure needs to be scientifically investigated and improved.
Hence, the outstanding scientific contributions of this joint project inspire other research groups and disciplines in reaching higher efficiency, better performance and longer operation times within the important field of CO2 reduction and reuse.
Implications for practice
The joint project gained scientific and to a large degree also practical knowledge which can directly be transferred (PEM) or is even currently being transferred (SOFC and CO2) to a more industry-relevant level. Thanks to the wide range of topics addressed by the subprojects (PEC, CO2, PEM, SOFC) a host of stakeholders and interest groups can now benefit in practice from the successful implementation of the relevant technologies and the sustainability assessment:
- Politicians and economists;
- CO2 emitting industries;
- Gas providers and natural gas grid operators;
- The fuel cell industry;
- End consumers.
Technology transfer itself has already been started for technologies such as PEM, SOFC and CO2 methanation, because the subprojects also generated a large share of practical knowledge. The direct effects for real-life applications are as follows:
- CO2 methanation catalysts are currently implemented in a high efficiency demonstration plant in Switzerland (CO2 reuse for CO2 savings);
- Novel catalyst concept for SOFC provides a more reliable system, economically more attractive to house owners, because of reduced CO2 emissions, longer life span with reduced resource consumptions (CO2 savings);
- The critical operation condition of PEM fuel cells is improved, which can have an impact on the decision to buy a fuel-cell-powered instead of a combustion based car (CO2 savings).
Reduction & reuse of CO2: renewable fuels for efficient electricity production
The joint project consists of five research projects
- Dr. Andreas Borgschulte, Departement Mobilität, Energie und Umwelt, EMPA Dübendorf
- Prof. Anders Hagfeldt, Laboratoire de photonique et interfaces, EPF Lausanne; Prof. Jürgen Schumacher
- Dr. Andre Heel, Institute of Materials and Process Engineering, ZHAW Winterthur
- Prof. Jürgen Schumacher, Institute of Computational Physics, ZHAW Winterthur; Dr. Felix Büchi
- Vicente Carabias, Institut für Nachhaltige Entwicklung, ZHAW Winterthur; Dr. Silvia Ulli-Beer; Dr. Christian Zipper