Research focus: Hydrogen
The important role of hydrogen in the transition
"Green hydrogen is the oil of tomorrow."
It is generally accepted that we need alternatives to fossil fuels in order to advance climate protection and achieve long-term success in energy system transformation. The top priority is to reduce CO2 emissions. One possible way to achieve this involves a national supply of carbon-neutral hydrogen ("green" hydrogen) and its derivatives.
Measures to accomplish this goal have been outlined by the German Federal Government in its recently presented National Hydrogen Strategy. The strategy aims at a decarbonization on the basis of carbon-neutral hydrogen. For this purpose, hydrogen production plants with a total capacity of initially up to 5 GW need to be built. Hydrogen will thus become the key raw material and state-of-the-art hydrogen technology the core element of the energy transition.
Hydrogen as key raw material
Why do we need hydrogen for decarbonisation?
A major challenge of the energy revolution is sector coupling. If we take a look at all sectors (industry; transport; households; commerce, trade and services), it becomes clear that currently only around 20% of total energy consumption in Germany is covered by electricity, with the majority of the remaining consumption being accounted for by energy sources such as petroleum products (36%) and gases (25%).1 It is therefore essential that these energy sources in particular are going to be replaced by energy sources with lower or no CO2 emissions. Replacing them with climate-neutral electricity in order to completely decarbonize all sectors is, according to experts, neither technically nor economically feasible or reasonable, especially as electricity demand is expected to continue to rise. Example: The high ranges and payloads required in the transport sector, as well as the need for fast refueling, are barely feasible with battery powered engines.
According to current expectations, Germany's energy demand exceeds the expansion of renewable energies by a factor of two.2 This means that, according to current estimates, the expected primary demand cannot be met by the expansion of wind and solar power plants alone. Therefore, carbon-neutral energy sources are needed that also serve fields of application that are difficult to electrify. Here, electrolysis can be a central process and hydrogen can be the link between the electricity production and energy consumption.
Recognizing and developing the potential of hydrogen
Hydrogen as an all-rounder?
The element hydrogen is earth abundant, but it appears almost exclusively in chemical compounds such as water, acids, etc. Hydrogen is obtained by splitting water (H2O) into its components oxygen (O2) and hydrogen (H2) with the help of electric power (electrolysis).
At present, hydrogen is primarily used in the chemical industry as a raw material, e.g., for the production of fertilizer or in oil refineries for the refining of mineral oil. Hydrogen also plays an important role in the production of synthetic fuels.
In addition to direct use, hydrogen is also becoming increasingly important for the system integration of renewable energies due to its high storability and transportability. This opens up a wide range of applications for hydrogen, for example as propulsion energy for vehicles, ships and aircraft (power-to-fuel) or for electricity generation in power plants or fuel cells. Hydrogen and (chemical) energy carriers based on it therefore have great potential for implementation in a sustainable energy turnaround.
Challenges
The production of green hydrogen requires large amounts of renewable electricity and is still too expensive. Furthermore, the conversion to hydrogen-based plants requires high investments. As a result, competition with cheap fossil fuels and established generation and consumption technologies is fierce. “In order to drive the development forward and achieve cost degression, generation plants must be built on an industrial scale, and a corresponding scale in the production of CO2-free hydrogen must be achieved with a significantly growing sales market.”3
Solution: Research
In order to make hydrogen a flexible energy carrier/storage medium suitable for a wide range of applications, intensive research and development efforts in the field of innovative hydrogen technologies are still required.
Green hydrogen: Production of hydrogen by electrolysis, using electricity from renewable energy sources such as wind and solar.
Blue hydrogen: hydrogen produced with CO2 capture and storage. This is considered CO2-free if no CO2 escapes into the atmosphere during production.
Grey hydrogen: During its production, CO2 is produced, as it is obtained from fossil energy sources such as natural gas.
Hydrogen research at the Max Planck Institute for Chemical Energy Conversion
„We forge the tools that others can use to build the technologies.“
One of our tasks at MPI CEC is to conduct fundamental research into hydrogen, its production, and its storage and utilization possibilities. Following Max Planck's philosophy "Knowledge must precede application” we want to break down in detail what basic understanding is needed to develop efficient technologies.
"We have to forge the tools that others can use to build the technologies," says Prof. Robert Schlögl, Managing Director at the MPI CEC and vice chairman of the National Hydrogen Council of the federal government.
Research at the MPI CEC focuses on hydrogen production by electrolysis (water splitting), chemical CO2 reduction, the conversion of hydrogen into other chemical products and transportable and more storable forms, such as methanol or ammonia. We also deal with the optimization of these processes and pay special attention to the different forms of catalysis. Catalysis is an essential technology for electrolysis and other conversion processes. We are therefore trying to develop catalysts that consist of both sustainable and cost-effective materials.
However, hydrogen production using electrolysis is still a very cost-intensive process, as the facilities are not yet available on a large scale. Although the production of the corresponding plants is not a task for basic research, but for our industrial partners. But we can make an important contribution to the catalysts required for this. "Since there are special requirements for the catalysts, comprehensive basic knowledge is essential here as well," says Schlögl. In the production of catalysts, chemists follow certain "recipes" that involve highly complex reactions. At the MPI CEC we try to understand catalysts on an atomic level and to describe on a quantum mechanical level why a reaction takes place in a certain way. This is still a great challenge for science.
Projects and cooperation in hydrogen research
The MPI CEC is also involved in many different cooperation and research projects on hydrogen. For example in the Kopernikus Power-to-X projects, which aim to develop technologies and processes that can convert and store renewable energy.
Energy Converting Enzymes
The group „Energy Converting Enzymes“ (Dr. J. Birrell) studies enzymes (biological catalysts) including those that carry out reactions such as hydrogen oxidation and proton reduction. The main focus is in understanding their mechanisms to provide chemists with information to make better industrial catalysts based on earth abundant metals.
The group also works with groups in Ruhr University Bochum to integrate hydrogen converting enzymes (hydrogenases) into electrode materials in order to generate hydrogen fuel cells, water electrolyzers and hydrogen biosensors.
The main focus of the group is characterizing [FeFe] hydrogenases, the most active class of hydrogenases, using a wide range of electrochemical and spectroscopic methods. This work is done in collaboration with numerous members of MPI CEC (including former director Prof. Wolfgang Lubitz) as well as multiple national and international partners. In the last few years they have come very close to having a comprehensive picture of the catalytic cycle in these enzymes.
Furthermore, the group is investigating the oxygen sensitivity of [FeFe]hydrogenases and the mechanism of a multifunctional [FeFe]hydrogenase from a thermophilic bacterium. This hydrogenase is able to produce hydrogen using multiple electron sources simultaneously. How this is achieved is unknown but solving the structure of this enzyme using cryoelectron microscopy may help to elucidate the mechanism.
In the future, the group will probably also deal with other hydrogen-related topics:
- Cryoenzymology of hydrogenases: studying enzymes at low temperature can slow down catalysis and trap unstable intermediates for structural and spectroscopic characterization.
- Thermostable hydrogenases for applications: hydrogenases from thermostable organisms could provide new opportunities for learning about enzyme mechanisms and producing useful devices with enhanced stability at elevated temperatures.
- Hydrogen to other products: ferredoxin and the NADH generated by certain hydrogenases could be used to make other products in biotransformations such as production of methanol or fixation of CO2 as CO or formate.
- H2 sensors: hydrogenases react extremely quickly with H2 and so they can be used as extremely sensitive H2 biosensors.
- Factors involved in substrate/product selectivity: enzymes are often extremely selective and only react with a single substrate to generate a single product while industrial catalysts may produce additional unwanted side-products. Comparing enzymes with industrial catalysts may provide an understanding of the important factors for selectivity.
EPR Research group
The EPR Research group (Dr. A. Schnegg) studies the structure-function relationship of earth abundant transition metal ion catalysts, which are relevant for the development of novel electrolysers (H2 formation) and fuel cells (H2 utilisation) for a future hydrogen economy.
- Photosynthesis provides the blueprint for harvesting solar energy to generate stable and energy-rich solar fuels (hydrocarbons). To obtain a detailed picture of the water splitting process in plants, we study the dynamics and binding positions of the involved substrate water molecules in the active protein complex, photosystem II (PSII). Advanced hyperfine spectroscopy is used to monitor the exchange of 17O labelled water molecules in the binding pockets of the water-splitting complex therein.
- Hydrogenases are highly relevant in hydrogen conversion and catalyse the formation and oxidation of molecular hydrogen,. The active site of these enzymes contains the abundant metals nickel and/or iron, which catalyse H2 conversion at zero overpotential and ambient conditions. This is why hydrogenases serve as model for the development of cheap and efficient catalysts to be used in future electrolysers and fuel cells.
- Iron and cobalt single atom catalysts (SAC) embedded in carbon matrices are promising candidates to replace platinum-based catalysts for the oxygen reduction reaction in polymer-electrolyte-membrane (PEM) fuel cells. Combined in situ EPR and Mössbauer spectroscopy is used for the identification of active sites and the assignment of oxidation states and coordination environments of iron and cobalt macrocyclic SACs. Further studies are devoted to the effect of co-catalysts on the stability of FeNC SACs.
- To replace noble metals in cost effective polymer-electrolyte-membrane (PEM) electrolysers, heterogeneous transition metal ion catalysts are explored. Special emphasis is devoted to catalysts operating in acidic media, since these conditions are favoured from economic and engineering perspectives. Combined electrochemistry and EPR spectroscopy is employed to learn about the stability and working mechanisms of these materials.
Multiphase Catalysis
The group Multiphase Catalysis (PD Dr. A. Vorholt) is focussing on different scales of catalysis - to use hydrogen for storing energy and materials.
The effective use of hydrogen and therefore the degree of efficiency is dependent on the catalyst for the conversion but also on the system it is deployed in. Therefore, the different scales for hydrogen conversion are investigated:
- from the molecular catalyst level
- to the phase level in which the catalyst is solvated
- to the process level which include separation steps
The envisaged reactions are the fixation of CO2 and the build-up of carbon chains for fuels, energy molecules, synthesis building blocks and new materials.
References
[1] AG Energiebilanz e.V.: Auswertungstabellen zur Energiebilanz für die Bundesrepublik Deutschland 1990-2018; Umweltbundesamt: Energieverbrauch nach Energieträgern und Sektoren. Link
[2] Fraunhofer-Institut für System- und Innovationsforschung ISI, Karlsruhe; Fraunhofer-Institut für Solare Energiesysteme ISE, Freiburg: Eine Wasserstoff-Roadmap für Deutschland
[3] BMWi – Artikel „Wasserstoff: Schlüsselelement für die Energiewende“ https://www.bmwi.de/Redaktion/DE/Dossier/wasserstoff.html