An oxygen reduction reaction electrocatalyst tuned for hydrogen peroxide generation based on a pseudo-graphite doped with graphitic nitrogen

Abstract

The carbon material, GUITAR (pseudo-graphite from the University of Idaho thermolyzed asphalt reaction) can be doped with nitrogen in two prevalent forms. In a previous study N(py)-GUITAR had a predominance of pyridinic and pyrrolic moieties with no graphitic nitrogen. In this study N(g)-GUITAR contains a 9.7 % N atomic abundance, with that fraction consisting of 72.3 % graphitic, 23.7 % pyridinic, and 0 % pyrrolic nitrogen. The two materials allow for the examination of hypotheses regarding the importance of the three different nitrogen moieties in the oxygen reduction reaction (ORR). In the previous investigation, the lack of graphitic nitrogen of N(py)-GUITAR gave a preferred pathway of 4e- ORR to H2O. In this investigation, N(g)-GUITAR gave a 2e- ORR pathway to H2O2. This was elucidated by current efficiency and hydrodynamic voltammetry studies. The high predominance of graphitic nitrogen confirms the hypothesis regarding 2e- vs. 4e- ORR pathways with N-doped carbon materials. N(g)-GUITAR was also evaluated for parasitic pathways for H2O2 production. At -0.95 V vs. Ag/AgCl the combination of current efficiency for H2O2 is 96 % in 0.05 M Na2SO4 with a production rate of 4.9 mg cm-2 h-1, is the highest reported in the literature. This indicates possibilities for water purification and treatment applications, which require 10 to 250 mg L-1, depending on conditions.