Integration of Non-Platinum Metal Group Catalysts with Bilirubin Oxidase into a Hybrid Material for Oxygen Reduction Reaction: Interplay of Chemistry and Morphology
Authors: Rojas-Carbonell Santiago , Babanova Sofia , Serov Alexey , Artyushkova Kateryna , Workman Michael J , Santoro Carlo , Ulyanova Yevgenia , Singhal Sameer , Atanassov Plamen 
Published: February 2020

The fuel cell technology has the capabilities to satisfy the high-energy demand that our modern lifestyle requires. Fuel cells have been used for transportation, stationary power systems and electronic devices among others. One of the main concerns regarding this promising technology is the high cost and low availability of some of the materials that are their constituents, specifically the cost of the catalysts. Looking forward to solve this problem, several groups have developed alternative catalysts. Non-platinum metal group catalystsare a novel type of materials, which are self-supported structures constituted of metal, nitrogen and carbon [1]. They have been developed to electrochemically catalyze the reduction of oxygen reduction, which occurs at the cathodes of the majority of fuel cells.Those materials have been proven successfully for the operating conditions of the fuel cells, where the pHs are usually highly acidic or alkaline. In order to explore those materials for other applications, such as biological fuel cells, the catalytic activity has to be dramatically improved since biological fuel cells operate at neutral pH. For this reason, we proposed the integration of non-platinum group material with an enzymatic catalyst, which carries out the same reaction but its optimal activity is in circumneutral environment.
Non-platinum based catalyst was synthesized by the Sacrificial Support Method (SSM) using iron nitrate and various carbon precursors [2]. This material was further integrated with bilirubin oxidase, an enzyme capable of performing oxygen reduction reaction (ORR). In order to provide efficient integration of the two catalysts, we characterized the specifics of the Non-PGM materialas shown in the Figure 1, where the current density at 200mV of the hybrid catalyst and Non-PGM alone are presented.
The two main characteristics of the non-PGM that were studied are morphology and chemistry. Starting with the morphology, it is important to address what is the surface environment to which the enzyme will be binding. This surface environment was characterized by means of Scanning Electron Microscopy imaging (SEM), which was latter analyzed by discrete wavelet transformation[3]. The complexity of these surfaces can be appreciated in Figure 2, an SEM image of one of the tested catalysts. The chemical composition of the Non-PGMs was studied byX-ray photoelectron spectroscopy (XPS). It was found that the chemistry of the Non-PGMs, the morphology along with the surface area play an important role in the enhancement of the performance for the hybrid catalyst.
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[2] C. Santoro, A. Serov, C.W.N. Villarrubia, S. Stariha, S. Babanova, K. Artyushkova, et al., High catalytic activity and pollutants resistivity using Fe-AAPyr cathode catalyst for microbial fuel cell application., Sci. Rep. 5 (2015) 16596. doi:10.1038/srep16596.
[3] M.J. Workman, A. Serov, B. Halevi, P. Atanassov, K. Artyushkova, Application of the Discrete Wavelet Transform to SEM and AFM Micrographs for Quantitative Analysis of Complex Surfaces., Langmuir. 31 (2015) 4924–33. doi:10.1021/acs.langmuir.5b00292.

Figure 1