апрель 2019

Palladium-based anodic catalysts modified by conductive polymers and palladium-platinum cathodic catalysts for direct formic acid fuel cells

Kupiec K. R. <img src=" width="22px">Kupiec K. R. , Borodziński A.Borodziński A., Lin H.-M.Lin H.-M., Chiou Y.-J.Chiou Y.-J., Kędzierzawski P.Kędzierzawski P.
Химия и современные технологии
Abstract / Full Text

The goal of the study is to identify promising catalysts for electro-oxidation of formic acid and for electro-reduction of oxygen in direct formic acid fuel cells (DFAFC). For the electro-oxidation of formic acid it is intended to employ palladium based catalysts supported on conductive polymers-multiwall carbon nanotubes composites. For the electro-reduction of oxygen in direct formic acid fuel cell environment it is planned to use palladium-platinum based catalysts. Improvement of the DFAFC performance, and, especially, increasing of the resistance of palladium catalyst to CO poisoning is the subject of an intensive research.

Fuel cells operating on liquid fuels for small and medium scale applications have prospects of commercialisation, and low temperature DFAFC appear among the most promising in this respect. DFAFC has a number of advantages over other fuel cells: (i) higher power density, higher energy efficiency and higher electromotive force than methanol fuel cell, (ii) formic acid as a liquid is easy to handle, (iii) crossover flux of formic acid through Nafion® membrane is several times smaller than that of methanol. Palladium is a very effective formic acid electro-oxidation catalyst, however, it works perfectly in the very pure, and so, very expensive formic acid. In a formic acid of lower purity, palladium becomes gradually poisoned, mainly, by –CH3 group containing impurities including methanol, which are oxidized via adsorbed CO, blocking further reaction. Improvement of the CO resistance of the anodic catalyst, which can work with less expensive fuel, is the most important problem to be solved for wide implementation of DFAFC. It was found in literature, that Pt deposited on polyaniline (PANI) is resistant to CO poisoning, when employed as a catalyst of methanol electro-oxidation. It can be expected, that the same effect will be observed for Pd deposited on conductive polymers (CP). In the literature, the most intensively studied CP are: polyaniline (PANI) and polypyrrol (PPy). PANI has been successfully synthesized in formic acid displaying excellent conductivity. One of the main obstacle, occurring when conducting polymers are employed as catalyst support, is polymer switching into a state of lower conductivity, when the potential value is changed. This study has developed two approaches: (A) Application of conductive polymer – multiwall carbon carbon nanotubes (MWCNTs) composites as a catalyst support. In such a composite MWCNTs will provide necessary conductivity if the polymer is switched to the lower conductivity state; (B) Addition of a second conducting polymer to the composite. This can enlarge the potential range in which the composite will be well conductive.

There are only single works, where CP supported catalysts were tested in a fuel cell setup. This anode catalyst research for the first time (as to the PhD candidate knowledge) will study CPs supported Pd catalysts for formic acid oxidation in the formic acid fuel cell setup on the systematic basis.

DFAFC cathodes are subjected to unique conditions that originate from the so-called “formic acid crossover”. The decrease in the DFAFC cathode performance is mainly owing to formic acid crossover, in which formic acid is transported from the anode to cathode through a polymer electrolyte membrane (PEM). Pt-based nanoparticles are well known for their effective electrocatalytic activity in cathodic reactions. However, Pt-based catalyst is easily poisoned by impurities in formic acid of lower purity that is transported via crossover phenomenon. The goal for research on cathode electrocatalysts is to find the most attractive ratio of Pd:Pt for catalyst that will show selective oxygen reduction activity compared to formic acid oxidation.

The research include the preparation, structural characterization, and electrocatalytic analysis of investigated catalysts. The key tools used in the research are SEM, TEM, XRD, XPS and electrochemical analysis – CV and fuel cell tests.