Fuel cells that directly convert chemical energy into electricity meet the demands for the clean energy industry of the future, primary owing to their striking advantages of the high-energy conversion efficiency that is not limited by the Carnot cycle, low/zero emission, and reliable and simple structure. Currently, a barrier that limits the development of the conventional cation-exchange membrane direct liquid fuel cells (CEM-DLFCs) is that the CEM-DLFCs need additional base to offer both alkaline environment and charge carrier. We develop a Na+-conducting direct formate fuel cell (Na-DFFC) that is operated in the absence of added base shown in Figure 1. The Na-DFFC consists of a membrane electrode assembly (MEA), which is composed sequentially of an anode electrode, an ion exchange membrane, and a cathode electrode.
A proof-of-concept Na-DFFC yields a peak power density of 33 mW cm-2 at 60 ℃, proving the conceptual feasibility. Moreover, contrary to the conventional chlor-alkali process, this Na-DFFC enables to generate electricity and produce NaOH simultaneously without polluting the environment. The Na-DFFC runs stably during 13 hours of continuous operation at a constant current of 10 mA, along with a theoretical production of 195 mg NaOH.
Let us place the present fuel cell in a large-scale carbon dioxide conversion system, as described in Figure 3. Formate, as a solar fuel, can be easily derived from electrochemical reduction of carbon dioxide in comparison to the formation of other chemicals such as alkanes, alcohols, and carbon monoxide, primarily because the strong carbon-oxygen bond does not undergo complete dissociation. It has been reported that the no-noble metal catalysts, such as Co, Pb, Zn, and Sn, present a high activity toward formate production: the faradaic efficiency on Sn electrode can be as high as ~95%. Question is how to further utilize the formate effectively. The proposed Na-DFFC provides an alternative solution: the photosynthesized formate as a chemical energy carrier, enables to be directly converted into electricity via the Na-DFFC, allowing clean and high-energy conversion efficiency. More appealingly, contrary to the conventional chlor-alkali process that consumes electricity to produce base, the sodium hydroxide also could be yielded as a byproduct without both electrical consumption and environmental pollution. Overall, the Na-DFFC is capable of converting the atmospheric carbon dioxide to electricity and chemical feedstocks. This work presents a new type of electrochemical conversion device that possesses a wide range of potential applications.
This new sustainable technology has been highlighted as “producing electricity from existing chemical feedstocks without environmental pollution” by ChemistryViews, an authoritative magazine in the field of chemistry that is held by 16 continental European chemical societies.