Mesoporous Carbon Supported Ag-Based Catalyst for Anion Exchange Membrane Fuel Cell
Authors: Linge Jonas Mart , Erikson Heiki , Mooste Marek , Piirsoo Helle-Mai , Kaljuvee Tiit , Kikas Arvo , Aruväli Jaan , Kisand Vambola , Tamm Aile , Kannan Arunachala Mada , Tammeveski Kaido 
Published: September 2023

The human population is growing and needs more energy for optimal life. Since fossil fuel consumption is no longer accepted, new green energy sources are sought after, found, and further developed. One such energy carrier is hydrogen, which is used as fuel in various low-temperature proton exchange membrane (PEMFCs) and anion exchange membrane fuel cells (AEMFCs).1 Unfortunately, these technologies are expensive due to the application of electrochemically active platinum-based catalysts. Thus, to make fuel cell technology more affordable: cheaper, more active, and more stable, non-Pt catalysts are researched and developed.
For example, Ag has shown comparable and competitive results to Pt-based catalysts in an alkaline environment when used in AEMFCs.2 In addition, Ag is nearly 50 times cheaper than Pt. In this work, Ag nanoparticles were deposited, using two different reducing agents – NaBH4 and hydrazine hydrate, onto two novel mesoporous engineered carbon support (ECS) materials with a well-defined and uniform mesoporous structure with pore sizes of 8 and 35 nm for ECS004601, and 7 and 25 nm for ECS004201 (Pajarito Powder, LLC). For comparison, conventional Vulcan carbon XC-72R was used as a support to see whether the ECS supports promote better dispersion of Ag particles.
SEM micrographs confirm that the synthesized Ag particles covered the mesoporous carbon support homogeneously. According to the XRD analysis, the average size of Ag crystallites remained between 19 and 28 nm. According to the thermogravimetric analysis, electrochemical Ag stripping, and SEM-EDX analysis, the amount of Ag in the catalysts after synthesis remained close to the nominal 40 wt%. Figure 1a shows that half-wave potentials (E
1/2) remained in the range from -0.29 V to -0.37 V vs SCE, where catalyst Ag/4201_HH had the most positive E
1/2, and bulk Ag electrode had the most negative. The electron transfer number n was close to four for all the Ag-based catalysts. Catalysts Ag/4201_HH and Ag/4601_BH4 had the biggest mass activities and showed good stability during 1000 potential cycles, where E
1/2 shifted only by 30 mV for Ag/4601_BH4 and 36 mV for Ag/4201_HH. Thus, these materials were tested in H2/O2 AEMFC where Aemion+ anion exchange membrane was employed and Figure 1b shows that the peak power density for Ag/4201_HH was 243 mW cm-2 and for Ag/4601_BH4 310 mW cm-2. Therefore, these materials are promising cathode catalysts for the AEMFC application.3

References

A. Sarapuu, E. Kibena-Poldsepp, M. Borghei, K. Tammeveski, Electrocatalysis of oxygen reduction on heteroatom-doped nanocarbons and transition metal-nitrogen-carbon catalysts for alkaline membrane fuel cells, Journal of Materials Chemistry A 6(3) (2018) 776-804.

H. Erikson, A. Sarapuu, K. Tammeveski, Oxygen Reduction Reaction on Silver Catalysts in Alkaline Media: a Minireview, Chemelectrochem 6(1) (2019) 73-86.

J. M. Linge, H. Erikson, M. Mooste, H-M Piirsoo, T. Kaljuvee, A. Kikas, J Aruväli, V. Kisand, A. Tamm, A. M. Kannan, K Tammeveski, Ag nanoparticles on mesoporous carbon support as cathode catalyst for anion exchange membrane fuel cell, International Journal of Hydrogen Energy (2023).

Figure 1