|A CO2-H2 power supply system as envisioned by the Leibniz team. Click to enlarge.|
Researchers at the Leibniz Institute of Catalysis in Rostock, Germany have developed a feasible process for the on-demand release of hydrogen from formic acid (HCO2H) without the need for the high-temperature reforming process usually involved in other thermochemical hydrogen generation systems.
Björn Loges, Albert Boddien, Henrik Junge, and Matthias Beller report in the journal Angewandte Chemie that this hydrogen, generated at room temperature, can be directly introduced into fuel cells.
Our previous work on the development of low-temperature hydrogen generating systems used alcohols as feedstock. More recently, we had the idea to apply carbon dioxide as storage media for hydrogen. Based on the catalytic processes of formation and decomposition of formic acid, a power supply system should be possible.—Beller (2008)
In the presence of an amine (e.g. N,N-dimethylhexylamine) and with a suitable catalyst (e.g. the commercially available ruthenium phosphine complex [RuCl2(PPH3)2]), formic acid is selectively converted into carbon dioxide and hydrogen at room temperature.
A simple activated charcoal filter is enough to purify the hydrogen gas for use in a fuel cell. The use of formic acid for hydrogen storage allows the advantages of established hydrogen/oxygen fuel cell technology to be combined with those of liquid fuels. Formic acid is nontoxic and easy to store. Because formic acid can be generated catalytically from CO2 and biomass-derived hydrogen, the cycle can be CO2 neutral in principle.
...we have shown for the first time the generation of hydrogen from formic acid amine adducts at such high rates at room temperature with the commercially available complex [RuCl2(PPh3)3]. Compared to previously known organic hydrogen generating systems the system presented can be run at low temperatures without the need of high-temperature reforming processes. The hydrogen produced can be directly used in fuel cells, thus combining the advantages of liquid fuels and established H2/O2 fuel cells. This might be interesting for new applications in portable electric devices.—Beller (2008)
Electrochemical Reduction of CO2. The basic process of the electroreduction of CO2 to organic chemicals such as formic acid, methanol and methane has been known for more than a century. Researchers in Canada have demonstrated the reduction of CO2 to formate (HCO2-) in a trickle-bed continuous electrochemical reactor under industrially viable conditions.
Based on their laboratory work at 10-100 A scale, Prof. Colin Oloman, of the University of British Columbia, and Dr. Hui Li, of the Institute for Fuel Cell Innovation, National Research Council, conclude this type of reactor could potentially be used as the basis for a commercial operation, presuming issues of cathode stability, formate crossover to the anode, and fluid flow distribution can be resolved.
On the basis of a crude (single-cell) reactor model, we have developed conceptual flowsheets of two process options for converting 100 tonne of CO2 into formate and/or formic acid per day. Steady-state material and energy balances indicate that these options are technically feasible, provided the problems mentioned above are not “show-stoppers”. Rough economic calculations predict a sample return on investment in the range of about 0-40% per annum, depending on the cost of electricity (0.01-0.10 US$ kWh-1) and the value of carbon credits (10-1000 US$t-1 (CO2)), while assuming that all products are sold at the prevailing bulk chemical market prices.—Oloman (2008)
Matthias Beller, et. al. (2008) Controlled generation of hydrogen from formic acid amine adducts at room temperature and application in H2/O2 fuel cells, Angewandte Chemie International Edition 2008, 47, No. 21, 3962-3965, doi: 10.1002/anie.200705972
Colin Oloman and Hui Li (2008) Electrochemical Processing of Carbon Dioxide, ChemSusChem 18 Apr 2008 doi: 10.1002/cssc.200800015