FuelCellsWorks

Utilizing carbon dioxide as an energy source with the aid of sunlight is the goal being pursued in a new research project for recycling of greenhouse gases. Researchers from BASF, Energie Baden-Württemberg AG (EnBW), Heidelberg University and Karlsruhe Institute of Technology (KIT) are seeking to convert CO2 into a fuel for fuel cells or retrofitted internal combustion engines – a step towards implementing environmentally conscious mobility technologies and simultaneously an alternative to existing carbon dioxide storage plans. The Verbund project “Solar2fuel” belongs to the “Forum Organic Electronics” excellence cluster and is being sponsored by the Federal Ministry of Education and Research (BMBF) with more than €1 million over two years.

While public discussion has so far centered mainly on the underground storage of carbon dioxide, the “Solar2fuel” project is focusing on the direct utilization of carbon dioxide. In this project, the carbon in carbon dioxide is converted into climate neutral fuels with the aid of sunlight. “A photocatalytic process of this nature could open up new ways of generating easy-to-handle energy sources,” says Prof. Dr. Michael Grunze of the Physical-Chemical Institute of Heidelberg University. The aim is to combine approaches based on nanotechnology and material research with catalytic processes.

The scientists at Heidelberg University are cooperating with BASF experts headed by Dr. Jan Schoeneboom to develop an air and light stable combination of dyes and functionalized nanoscale semiconductor particles. Under these conditions, sunlight can be absorbed in the optimal range with the aid of organic dyes and supply energy for the conversion of carbon dioxide. Photocatalysis is therefore used to convert the carbon dioxide – generated for example by combustion processes in a power plant – together with water into the energy source methanol. In this way, sunlight can be used directly as a regenerative energy source in the recycling of CO2 – a process not unlike plant photosynthesis but, the researchers hope, much more efficient.

The experts at EnBW are investigating the energy, emission and cost balances of the overall process – from the power plant waste gas through the actual photocatalysis up to the utilization of the products. The cost of supplying carbon dioxide from power stations is also being analyzed. “With these activities, EnBW is attempting to establish the conditions under which such processes could be economically viable,” explains Prof. Dr. Wolfram Münch, Head of the Research and Innovation Department at EnBW.

The technical engineering aspects of “Solar2fuel” are being implemented by KIT scientists under the supervision of Prof. Dr. Henning Bockhorn. These experts are investigating the physico-chemical and process technology aspects within the overall process. Based on an analysis of the overall system, the design of a photochemical reactor is to be developed and simulated using computer assisted methods.

In the “Forum Organic Electronics” excellence cluster sponsored by the Federal Ministry of Education and Research, university and non-university research institutes are cooperating with industry in pursuing future-oriented developments in the field of organic electronics. Activities relating to the “Solar2fuel” project commenced in October of last year, BASF serves as coordinator for the consortium.

Crab shells provide a cheap and convenient template to make high performance carbon electrodes for energy storage and conversion, say Chinese scientists.

Carbon materials have many potential applications, including as electrodes in supercapacitors and fuel cells. The pore structure is known to affect their physicochemical properties and is normally controlled by using a porous hard template such as zeolite or silica. But the process usually involves using hydrofluoric acid to remove the templates, which can be complex and costly.

A research group from Fudan University, led by Yong-Yao Xia, has demonstrated that crab shell has a well aligned porous structure at the microscopic level. Exploiting this unique structure, they have generated porous carbon nanofibre arrays by combining the hard crab shell template with an established soft templating method. ‘Biological templates are generally abundant, renewable, inexpensive and environmentally benign compared to artificial templates,’ explains Xia.

After burning the crab shell in air, the porous template mainly consists of calcium carbonate. Adding a soft copolymer template and resol precursor forms the carbon framework. Heating under nitrogen gas removes the soft template and the hard template can be dissolved in hydrochloric acid.

‘The crab shell hard template is not only easy to remove but also hierarchically porous,’ says Rui Zhang, an expert in porous carbon materials at the Shanghai Institute of Technology. The templated carbon nanofibre arrays retain this hierarchical porosity, forming pores of three sizes. The largest result from the packing of nanofibres, the medium pores from voids between the nanofibres and the carbon nanofibres themselves contain the smallest pores.

The pore structure is suitable for charge storage by ion adsorption/desorption as an electrode material for supercapacitors or platinum/palladium catalyst loading for fuel cell applications, says Xia. Aided by the large surface area and complex structure, Xia’ material shows excellent results in both cases.

Xia’s team is now using crab shell to template other porous materials as well as investigating alternative shellfish templates.

Erica Wise