Decarbonization of the energy sector is a topic of paramount importance to avoid irreversible global warming. Hydrogen has been considered as the most suitable option to replace fossil fuels in industrial, residential and transport applications. However, hydrogen production has been almost limited to the reforming of hydrocarbons, which release large amounts of CO2, thus requiring several downstream purification processes.

Catalytic methane decomposition consists of the low-temperature cracking of methane, producing only COx-free hydrogen and solid carbon. This process has the unique potential to make the swift transition for a fully decarbonized economy and beyond: the methane decomposition of biomethane removes CO2 from the atmosphere at competitive costs. Yet, industrialization of catalytic methane decomposition has been hindered by the insufficient stability assigned to catalyst deactivation due to carbon clogging.

This article reviews not only the main accomplishments on methane decomposition since it was firstly reported, but also addresses technical barriers that have hindered its industrialization. Unlike other previous reviews that focused mainly on catalysts, more attention was put on the reactor design, catalyst regeneration strategies and processing of products (hydrogen purification and economic overview). The goal is to identify challenges and provide solutions for the industrialization paradigm that methane decomposition has faced up to now.

Metal-Supported (MS) architecture offers various advantages over state-of-the-art ceramic supported SOCs, such as high tolerance towards thermal/redox cycling that are key features for flexible and reliable operation in high temperature fuel cell and electrolysis applications. Our target is to develop Proton-conducting Ceramic Cells (PCC) in MS architecture, of which combination can provide potentially high performances, mechanical stability, and flexibility for wide range of electrochemical applications. The key challenge in the development of MS-PCC is to find a feasible process to fabricate gas-tight electrolyte on the porous metal substrate without degrading the metal support and the electrolyte. Our strategy is implementing multilayers combining wet chemical processes below 1000°C for the functional electrode and dry Physical Vapor Deposition (PVD) techniques below 800°C for the gas-tight electrolyte coating. In this paper, we present our recent results in the development of MS-PCC half cells. The materials selection for MS and PCC components, functional layer processing, and electrolyte layer deposition techniques are discussed.

A game-changer low temperature catalytic methane decomposition process proved already >2500 h of continuous operation at 550°C with a constant catalyst productivity of 0.64 gH2/gCat/h. But the experiment is going on, aiming at reaching over 6000 h of fully stable operation, by September 2023; at that moment the technology will reach the stability milestone for becoming a commercial solution.

The methane decomposition membrane reactor operates between 550°C and 700°C producing pure hydrogen.

The carbon by-product is >90 % graphitic, which is a quite valorized carbon and especially suitable for making electric conductive carbon paints, electrodes for electrochemical devices, bipolar plates for PEMFC (polymer electrolyte membrane fuel cell) and redox flow batteries, anodes of sodium-ion batteries, among a variety of other high-value applications. But these carbon particles of ca. 100 μm can also find use for making concrete, asphalt for streets and fertilizers for soil. However, the most amazing thing is that this carbon by-product can be tuned for its properties modifying the catalyst and changing the operating conditions, getting the best of the two products from the methane decomposition reaction.

A research team led by Adélio Mendes, researcher at the Laboratory of Process Engineering, Environment, Biotechnology and Energy (LEPABE) at the Faculty of Engineering of the University of Porto (FEUP), has just secured funding under the Horizon 2020 program of the European Union, with a total value of 3.5 million euros, to be applied in the development of a technology that allows the production of energy without the emission of greenhouse gases/pollutants.

The researchers want this technology to be low cost, sustainable, fast to implement, able to be used in stationary and mobile applications and always available to be used when needed.

“From a perspective of optimizing the project, I believe that we can still aim for this technology not only to not emit polluting gases, but to be able to remove them from the atmosphere”, admits Adélio Mendes.

And how does it all work? Through the decomposition of biomethane, in which the carbon dioxide collected by the biomass is transformed into charcoal, mimicking the natural process.

This project is studying the development of a technology capable of converting methane into coal and hydrogen in a sustainable way.​

Adélio Mendes, full professor at the Department of Chemical Engineering at the Faculty of Engineering of the University of Porto (FEUP), is developing the 112CO2 project with the aim of developing a green hydrogen production technology at competitive costs.

The idea is to transform biogas into coal and hydrogen at lower costs than hydrolysis, and more competitive compared to the conventional process of producing hydrogen from natural gas, taking into account the costs related to the removal and sequestration of the carbon dioxide produced during this reaction.

“We are facing an absolutely disruptive process that promises not only not to emit carbon dioxide in the production of hydrogen, but also to remove it from the atmosphere”, Prof. Adélio discloses.

This technology could be applied in engines of large vehicles such as trains, trucks and even cargo ships, and, in addition to the low cost, it will also have the ability to capture carbon dioxide from the atmosphere.

According to Adélio Mendes, this technology will allow the removal of one part per million of carbon dioxide from the atmosphere per year.

The 112CO2 project is funded by European funds under the Horizon 2020 programme.

Methane decomposition (MD) reaction, also known as methane pyrolysis, allows the conversion of methane from natural gas or biomethane into solid carbon and hydrogen with high purity:

CH4 → C (s) + 2H2 ΔH0 = 75.3 kJ mol-1

This reaction has the unique feature of being 100% selective. Apart from allowing the swift decarbonization of the energy, when biomethane is used, this reaction has the power to remove CO2 from the atmosphere as it produces H2 at very competitive costs. This technology enables using the present storage and distribution infrastructure for natural gas and produces H2 to be used locally as a fuel for electricity/ heat or as feedstock for chemical industries (steel production, ammonia synthesis, reversal petrochemistry, etc.).

Considering only the price of the raw materials, H2 from the decomposition of natural gas costs 1.9 €/kg, while biomethane-derived H2 costs 2.2 €/kg. At the present prices of CO2 allowances, >60 €/ton, this process saves 0.54 €/kg of H2. The MD of biomethane removes CO2 from the atmosphere. Assuming a cost for the direct air capture of CO2 of 150 €/ton and for its sequestration of 50/ton, per 1 kg of H2 produced, 0.60 € are saved in capture and sequestration of CO2.

The industrialization of catalytic MD has been hindered so far by the extremely fast catalyst deactivation, which is caused by the inevitable coverage of catalytic sites by the formed solid carbon. Competing institutions/companies are developing high temperatures MD processes involving either metal liquid reactors or reactors using carbon catalyst particles; however, these approaches are energy-intensive, dangerous to operate and display low catalytic activity.

112CO2, a FET-Proactive project, aims at developing a disruptive low temperature (ca. 550 °C) methane decomposition process, using abundant and cheap metallic catalysts. Briefly, the designed reactor uses Ni-based catalysts, which are very active but need to be cyclically regenerated. It is expected to reach >0.45 gH2 gCat -1 h-1 and stable for at least 10 000 h.

The project, which has started in September 2020, gathers some of the finest EU research laboratories and companies, including University of Porto, author of this new MD concept; Pixel Voltaic Lda., which is a spin-off company from UPorto, responsible for designing the process lab prototype; CSIC to synthetize the catalysts; DLR to develop proton conducting ceramics for efficient and cost-effective H2 purification; EPFL responsible for the dissemination activities; Paul Wurth S.A. and Quantis for performing life cycle assessment and economic analysis.

As explained by Adélio Mendes, professor at the University of Porto and project coordinator: "preliminary results allowed to reach a maximum catalytic activity of 3 gH2 gCat -1 h-1 and proved that the cyclic regeneration allows keeping the catalyst at its maximum catalytic activity. Initial experiments demonstrated worldrecord stabilities, using a compact reactor loaded with commercial and non-optimized catalysts." 112CO2 also proposes an ambitious communication strategy, aiming to involve stakeholders, investors, researchers, youngsters, and students for this emergent technology.

112CO2 project has received funding from the European Union's Horizon 2020 research and innovation Programme under the grant agreement No 952219.

Adélio Mendes, Full Professor from University of Porto and coordinator of 112CO2 project, describes the concept of low temperature catalytic methane decomposition for COx-free hydrogen production.

The world needs a disruptive tech-nology to quickly decarbonise the energy sector; the success of this technology critically depends on its social acceptance, sustainability, low-cost and fast implementation. The 112CO2 team believes to have this technology in place, the so-called methane decomposition is required for the cost-effective production of carbon-free hydrogen.

Methane decomposition for COx-free hydrogen production

Methane decomposition (MD) reaction converts methane from natural gas or biomethane into solid carbon and hydrogen. With the advantage of being 100% selective, this reaction has the power to produce clean hydrogen and remove atmospheric carbon dioxide at competitive costs. The state-of-the-art process for producing hydrogen from MD uses a moving bed reactor loaded with coal pellets, running at ~1400°C. The main objectives within the framework of 112CO2 are to bring the temperature down to 550°C and produce pure hydrogen in a compact, transportable, cheap and stable reactor; low stabilities are an issue at low-temperature processes. The 112CO2 project started in September 2020 and gathers some of the most outstanding EU research laboratories and companies (UPORTO, CSIC, DLR, EPFL, Pixel Voltaic, Paul Wurth, Quantis).

“The main innovations that are being addressed within 112CO2 are: i) making the MD catalyst very active, stable and regenerable; ii) high temperature hydrogen electrochemical pumping and purification; and iii) demonstrate a compact and efficient reactor to be operated at low temperatures.”

The world needs a disruptive technology to very quickly decarbonize the energy; the success of this technology depends heavily on its social acceptance, sustainability and fast and easy implementation. The proponents of 112CO2 believe to have this technology. Imagine that a new chemical reactor would make possible to use methane, an easy to transport and to store fuel, either fossil, renewable or synthetic, for producing COx-free hydrogen in a cost-effective way. Imagine that this approach could be implemented swiftly, taking advantage of the present infrastructure. 112CO2 project is about producing hydrogen from low temperature methane decomposition (MD), a 100 % selective reaction - CH4 → C (s) + 2 H2. The use of methane from biogas allows actively to remove CO2 from the atmosphere (negative carbon balance) but, if using fossil methane, there will be no COx emissions. 112CO2 project aims at developing a low temperature MD catalyst, easy to regenerate and very active, > 0.45 gH2/gCat/h and stable for at least 10 000 h. 112CO2 proposes an innovative regeneration step based on the selective hydrogenation of the carbon attaching interface with the catalyst, allowing to release the coke particles and the recovery of the catalytic activity. Proponents succeed very recently to demonstrate, in a 500-h experiment, that this approach is possible and easily accomplishable. A membrane reactor, made of a stack of individual cells for producing hydrogen and a stack for pumping out this fuel cell grade hydrogen, will be developed for running at ca. 600 °C and to display > 0.05 gH2/cm3/h, an energy density comparable to the PEMFC. The proposed MD reactor is suitable for mobile as well as for stationary applications. 112CO2 project proposes also an ambitious communication strategy, aim at to involve investors, existing companies, researchers, youngsters, undergraduate and graduate students for this new technology and engage them in the urgent energy decarbonization endeavour.