Influence of platinum group metal-free catalyst synthesis on microbial fuel cell performance

Abstract

Platinum group metal-free (PGM-free) ORR catalysts from the Fe-N-C family were synthesized using sacrificial support method (SSM) technique. Six experimental steps were used during the synthesis: 1) mixing the precursor, the metal salt, and the silica template; 2) first pyrolysis in hydrogen rich atmosphere; 3) ball milling; 4) etching the silica template using harsh acids environment; 5) the second pyrolysis in ammonia rich atmosphere; 6) final ball milling. Three independent batches were fabricated following the same procedure. The effect of each synthetic parameters on the surface chemistry and the electrocatalytic performance in neutral media was studied. Rotating ring disk electrode (RRDE) experiment showed an increase in half wave potential and limiting current after the pyrolysis steps. The additional improvement was observed after etching and performing the second pyrolysis. A similar trend was seen in microbial fuel cells (MFCs), in which the power output increased from 167 ± 2 μW cm−2 to 214 ± 5 μW cm−2. X-ray Photoelectron Spectroscopy (XPS) was used to evaluate surface chemistry of catalysts obtained after each synthetic step. The changes in chemical composition were directly correlated with the improvements in performance. We report outstanding reproducibility in both composition and performance among the three different batches.

Enhancement of microbial fuel cell performance by introducing a nano-composite cathode catalyst

“…As expected, the onset potential remained similar for all catalysts independently of their loading. This agrees with the previously reported data [ 62 , 72 , 82 , 84 ]. The half-wave potential is highest for Fe-AAPyr of about +0.075 to +0.01 V (vs. Ag/AgCl) and the lowest is for AC of about −0.25 to −0.32 V (vs. Ag/AgCl).…”

“…In literature, PGM-free catalysts incorporated into cathodes and tested in membrane less MFCs using a buffer solution as overall or part of the electrolyte (maximum considered of 0.1 M PBS buffer concentration) showed performance between 150 and 280 μW cm −2 [ [74] , [75] , [76] , [77] , [78] , [79] , [80] , [81] , [82] , [83] , [84] , [85] , [86] , [87] , [88] , [89] , [90] , [91] , [92] ]. This big variation among the results in literature is mainly due to the different operating conditions utilized during the experimentations such as temperature, electrolyte adopted, cell design, anode/cathode ratio, altitude on sea level, etc [ 11 , 82 ].…”

“…[ 73 ] were also used as cathode materials due to their low-cost, high surface area, relatively high conductivity and durability in “harsh” and polluted environments. The performance of carbonaceous-based materials is very limited compared to PGM-free catalysts containing earth abundant transition metals such as Fe [ [74] , [75] , [76] , [77] , [78] , [79] , [80] , [81] , [82] , [83] , [84] ], Mn [ [85] , [86] , [87] ], Co [ [87] , [88] , [89] ] and Ni [ 87 , 90 , 91 ]. Therefore, carbonaceous materials are often used as support for the catalyst rather than be the catalyst itself.…”

“…phthalocyanine or porphyrins) in which a metal center is incorporated; iii) product of pyrolysis of a metal salt and an organic precursor. Pyrolyzed PGM-free catalysts are generally the most used for MFCs [ 84 ]. It was shown previously that Fe-based catalysts were most active among Co-, Mn- and Ni-based materials in both rotating ring disk electrode (RRDE) [ 87 ] and in working MFCs [ 82 ].…”

Oxygen Reduction Reaction Electrocatalysts Derived from Iron Salt and Benzimidazole and Aminobenzimidazole Precursors and Their Application in Microbial Fuel Cell Cathodes

“…It was shown before that pyridinic nitrogen and nitrogen coordinated to metal are species of extreme importance for ORR in acidic, neutral, and alkaline media. 69 , 95 …”