Green hydrogen could reach economic viability by co-production of valuable chemicals

© Credit: Hassan Tahini, ScienceBrush Design

It already works: there are several approaches to using solar energy to split water and produce hydrogen. Unfortunately, this green hydrogen has so far been more expensive than grey hydrogen from natural gas. A study by Helmholtz-Zentrum Berlin (HZB) and Technische Universität Berlin now shows how green hydrogen from sunlight can become profitable.

Part of the hydrogen is used to upgrade raw biomass-derived chemicals into high-value chemicals for industry. This co-production concept is very flexible; the same plant can be used to produce different by-products as required. We need to move away from fossil fuels as soon as possible in order to limit global warming. In the energy system of the future, green hydrogen will therefore play an important role in energy storage and as a renewable feedstock for the production of chemicals and materials for a wide range of applications.

At present, hydrogen is mainly produced from fossil natural gas (grey hydrogen). Green hydrogen, on the other hand, is produced via electrolysis of water using renewable energy. One promising approach is to use photoelectrochemical (PEC) devices to produce hydrogen using solar energy. However, hydrogen from PEC plants is much more expensive than hydrogen from (fossil) methane.

Full control over reactions

A team led by Fatwa Abdi (at HZB until mid-2023, now at City University in Hong Kong) and Reinhard Schomäcker (UniSysCat, TU Berlin) has now investigated how the balance changes when some of the hydrogen produced in a PEC device reacts with itaconic acid (IA) to form methylsuccinic acid (MSA), all within the same device. The starting material, itaconic acid, comes from biomass and is fed in. Methylsuccinic acid is a high priced compound and needed by the chemical and pharmaceutical industries. In the study, the team describes how to control the chemical reactions in the PEC device by varying the process parameters and the concentration of the homogenous rhodium-based catalyst, which is water-soluble and already active at room temperature. In this way, different proportions of hydrogen could be used for the hydrogenation of itaconic acid, selectively increasing or decreasing the production of methylsuccinic acid.

Plant becomes profitable from 11 percent hydrogen for MSA

With a realistic overall PEC plant efficiency of 10 percent and taking into account primary costs as well as operation, maintenance and decommissioning, pure hydrogen production remains too expensive compared to production from fossil gas. This is true even if the lifetime of the PEC plant is assumed to be 40 years.

This balance changes if the PEC reaction is coupled with the hydrogenation process. Even if only 11 percent of the hydrogen produced is converted to MSA, the cost of hydrogen drops to 1.5 € per kilogram, which is already at the same level as for hydrogen from methane steam reforming. And this is true even for a PEC plant lifetime of only 5 years! As the market price of MSA is significantly higher than that of hydrogen, more MSA increases the profitability. In the experiment, between 11 and up to 60 percent of the hydrogen could be selectively used to produce MSA.

In addition, a previous study has shown that co-production of MSA also reduces the so-called energy payback time, i.e. the time it takes for the plant to recover the energy that its production has consumed.

Co-production can be switched

The PEC plant can also be used to produce other co-products by simply changing the feedstock and the (soluble) catalyst: for example, acetone could be hydrogenated to isopropanol. "This is another major advantage of our concept of co-production. We have found a promising way to make solar hydrogen production economically viable," says Fatwa Abdi.

The study was carried out as part of the Berlin Cluster of Excellence “UniSysCat” (Unifying Systems in Catalysis) and supported by the Excellence Network initiative of the Helmholtz Association.

Original Publication:

Nature communications (2023): Solar-driven upgrading of biomass by coupled hydrogenation using in situ (photo)electrochemically generated H2, Keisuke Obata, Michael Schwarze, Tabea A. Thiel, Xinyi Zhang, Babu Radhakrishnan, Ibbi Y. Ahmet, Roel van de Krol, Reinhard Schomäcker & Fatwa F. Abdi,

Antonia Rötger

You might also be interested in

  • Dynamic measurements in liquids now possible in the laboratory
    Science Highlight
    Dynamic measurements in liquids now possible in the laboratory
    A team of researchers in Berlin has developed a laboratory spectrometer for analysing chemical processes in solution - with a time resolution of 500 ps. This is of interest not only for the study of molecular processes in biology, but also for the development of new catalyst materials. Until now, however, this usually required synchrotron radiation, which is only available at large, modern X-ray sources such as BESSY II. The process now works on a laboratory scale using a plasma light source.
  • Key role of nickel ions in the Simons process discovered
    Science Highlight
    Key role of nickel ions in the Simons process discovered
    Researchers at the Federal Institute for Materials Research and Testing (BAM) and Freie Universität Berlin have discovered the exact mechanism of the Simons process for the first time. The interdisciplinary research team used the BESSY II light source at the Helmholtz Zentrum Berlin for this study.

  • Watching indium phosphide at work
    Science Highlight
    Watching indium phosphide at work
    Indium phosphide is a versatile semiconductor. The material can be used for solar cells, for hydrogen production and even for quantum computers – and with record-breaking efficiency. However, little research has been conducted into what happens on its surface. Researchers have now closed this gap and used ultra-fast lasers to scrutinise the dynamics of the electrons in the material.