Pt-Based Chalcogenide As Cathodic Electrocatalysts for Proton Exchange Membrane FUEL CELL (PEMFC)
Authors: Moreno-Grijalva Grecia Isis , Alonso Gabriel , Oropeza-Guzman Mercedes Teresita , Gochi-Ponce Yadira 
Published: February 2020

Protonic exchange membrane fuel cells (PEMFC) are considered one of the most promising electric generator devices, using electrochemical system to asses the energy generation. Neverthless, there are some issues that require main interest, as it is the Membrane-Electrode Assembly (MEA). The MEA is considered the biggest challenge to improve within a fuel cell, considering that electrode reactions are the responsibles of charge transfer process. Since platinum is known as the best electrocatalyst and carbon nanostructured materials are usually employed as metal’s support [1], the interest in current fuel cells studies is because of platinum high cost and poor abundance.

Even though the electrocatalyst is the main concern to improve, it’s necessary to stand out the cathode, since the oxygen reduction reaction (ORR) takes place. The ORR has been studied among many research groups because of the complexity and its slow kinetics, which needs higher platinum loading, being the main drawback for fuel cells massive commercialization. So, the importance of finding new materials with extended lifetime that can decrease noble metal loading are some of the demands to accomplish, to make more affordable fuel cells. One of the materials proposed are the chalcogenides.

Due to the fact that Pt is known as the best electrocatalyst among metallic materials, chalcogenides Pt-based electrodes are recently studied because of their high and comparable Oxygen Reduction Reaction (ORR) activity in fuel cells. İn this work, a previously reported material has been synthesized from sulphur-platinum with tungstene varying the concentration to decrease the noble metal loading for the electrocatalyst. In the other hand, carbon nanotubes are synthesized by modified spray pyrolisis and used as electrocatalytic support. Later on, they will be deposited into a sustrate by electrophoretic deposition in order to achieve a highly dispersed surface and so, improve the kinetic performance of the electrocatalyst. Physical characterization and electrochemical results are presented to study the ORR activity and the efficiency of these systems.

In the last decades the chalcogenides of metallic centers [2] have proved to be very active for the ORR. Their main characteristics are: 1) tolerance to organic molecules when they do not poison the surface, 2) Selectivity to one and only one reaction in particular, 3) high catalytic activity to carry out the ORR, which is, a high electrical current per mass of catalyst must be generated from the ORR. It has been demonstrated that chalcogenides can function as catalysts in the oxygen reduction reaction in a fuel cell and in turn have high stability. It is well known that Pt-based catalysts are the most active for RRO. The addition of a chalcogenide such as S and Se are the most common used because they improve the activity and selectivity of the catalyst [3]. This background leads us to work with the previously synthesized PtxWySz reported by Gochi which shows a greater performance for the ORR than Pt/C [4].

As results, modified platinum (PtxWySz) exceeds the current density comapre to the commercial electrocatalyst (Pt/C) among the electrocatalytic activity. Eventhough the material is unsupported, PtxWySz does not showed any unfavourable activity. On the contrary, PtxWySz 1:6 shows higher activity in spite of having less platinum loading (figure1b). Besides, the increase of the electrochemical active area due to the addition of chalcogenide is notable as it is the more positive on-set potential (figure1a).

Figure 1