Oxygen Electroreduction on Nanoporous Carbons: Textural Features vs Nitrogen and Boron Catalytic Centers

Abstract

Porous carbons containing either B and N heteroatom (∼10 at.% each) or B‐ and N‐free were synthesized and used as ORR metal‐free catalysts. The number of electron transfer was close to 4 (3.94) regardless the presence or not of heteroatom‐based catalytic centers, and the onset potential reached 0.827 V (on Pt/C 0.888 V). The carbons were extensively characterized from the viewpoints of their surface chemistry and porosity. The results indicated that a high volume of small pores where oxygen can be strongly adsorbed enhances the ORR efficiency, positively affecting the number of electron transfer and the value of the onset potential. On carbons with moderate volume of ultramicropores, N and B catalytic centers compensate the porosity effect enhancing the performance. These two mechanisms of ORR can coexist leading to a very efficient process on metal free carbon‐based porous catalysts.

3D Carbon Materials for Efficient Oxygen and Hydrogen Electrocatalysis

“…Han et al recently synthesized a N/B aerogel that showed a more positive onset potential (0.994 V) than existing N/B‐doped carbons in alkaline, though still somewhat poorer than Pt/C in alkaline. Florent et al showed that a high volume of small pores that adsorb O 2 enhances the ORR efficiency, and that the presence of B also helps the onset potential, contrary to what was previously shown on B‐doped CNTs, though the performance is significantly poorer than Pt/C in alkaline. Yu et al also synthesized N/B‐doped aerogels and tested them in alkaline as well as acid.…”

“…The stability of the catalyst should be tested either in the form of their retention of activity after many cycles (upward of 10 000) or prolonged voltage holds (>1 00 00 s). Although tolerance to MeOH is often a metric that is used to assess the quality of metal‐free catalysts, it has become abundantly clear that heteroatom‐doped catalysts are not active for MeOH oxidation, and so do not suffer voltage loss due to MeOH crossover, exemplified by the majority of recent examples in the literature . It is apparent that this is now a largely meaningless metric for metal‐free catalysts, and all non‐PGM (Pt group metal) materials should be assumed to have good tolerance to MeOH cross‐over.…”

“…Indeed, given the number of possible sites in single heteroatom‐doped carbons already discussed, the addition of a second heteroatom complicates the picture somewhat. There are many recent examples in the literature of co‐doping with N of various different heteroatoms, including sulfur, phosphorous, boron, fluorine, and iodine …”

Exploring the Silent Aspect of Carbon Nanopores

“…This directed us to hypothesize that a hydrophobic surface (ethers are hydrophobic [92]) and small pores advance the oxygen reduction reaction by providing sites for strong adsorption of oxygen upon its withdrawal from an electrolyte, and in these pores, the reduction process is enhanced. To further support our hypothesis, we expanded the research to porous carbons containing heteroatom-based groups known to catalytically enhance ORR [54][55][56][57]. The introduction of N, S, and B to the carbon matrix was our goal, and the spatial geometry of To further support our hypothesis, we expanded the research to porous carbons containing heteroatom-based groups known to catalytically enhance ORR [54][55][56][57].…”

Engaging nanoporous carbons in “beyond adsorption” applications: Characterization, challenges and performance

“…Quite recently, the search expanded and nanoporous carbons have been also included in that quickly advancing quest. Similarly to their other applications, there are reports in the literature indicating the importance of the porosity [83][84][85][86][87][88] and oxygen adsorption on the nanoporous carbons [89][90][91][92] for achieving an efficient ORR. The latter is usually described by the electron transfer number, kinetic current density, and onset potential.…”