Highly Stable, Low-Cost Metal-Free Oxygen Reduction Reaction Electrocatalyst Based on Nitrogen-Doped Pseudo-Graphite

Abstract

There have been many advancements in the search for an oxygen reduction reaction (ORR) catalyst that exhibits strong performance and exceptional durability using low-cost materials. Although recent advancements have focused on matching or surpassing the ORR performance of Pt/C, exploring ways to improve the durability of electrocatalysts on longer time scales has not been adequately addressed. In this work, a high-performance and stable ORR electrocatalyst was produced using a simple nitrogen-doping protocol on GUITAR (pseudo-Graphite from the University of Idaho Thermolyzed Asphalt Reaction)-coated Ketjen black (N′-GUITAR/KB). X-ray photoelectron spectroscopy indicates selective doping of pyridinic and pyrrolic moieties (total N abundance of 0.9%). Voltammetric experiments in O2-saturated 0.1 M KOH indicate that the electrocatalyst is exceptionally stable and one of the highest performers regarding overvoltage and current density. The system maintained its electrocatalytic performance throughout the Department of Energy stress protocol, which consists of 30,000 convective cyclic voltammetry cycles in O2-saturated 0.1 M KOH. This remarkable stability, along with the low-cost synthesis, represents an important milestone in overcoming the challenges that prevent wide-scale adoption of fuel cell technology.

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

“…For that study, N(g)-GUITAR was deposited on Ketjen black particles and drop-cast onto the RDE disks. This follows a procedure developed in a previous investigation [15]. This was conducted by a colorimetric method [26].…”

“…Symbols J, J k , and ω are the current density, kinetic current density, and angular velocity, respectively. In the K-L equation, B is 0.62nFν 1/6 c O₂ D O₂ 2/3 , where F is Faraday's constant, ν is the kinematic viscosity of the electrolyte (0.01 cm 2 s -1 ), c O₂ is the bulk concentration of oxygen (1.20×10 -6 mol cm -3 ) and D O₂ is the diffusion coefficient of O 2 in 0.050 M Na 2 SO 4 (1.90× 10 -5 cm 2 s -1 ) [15,36].…”

“…For the RDE study, the graphitic nitrogen-rich N(g)-GUITAR electrocatalysts were deposited on Ketjen black particles as described in the experimental and previous studies [15]. In previous investigations, pristine GUITAR had n = 2.6 to 2.8 and a variant of an N-doped GUITAR (N´-GUITAR) which had a predominance of pyridinic and pyrrolic moieties, was found to have n = 3.6 to 3.7 [15]. The background corrected RDE linear sweep voltammograms (5 mV s -1 ) from 400 to 2400 rpm are shown in Figure 10A.…”

“…The 3-volt aqueous potential window is among the largest reported. GUITAR is grown using a chemical vapor deposition process, which allows for the fabrication of electrodes ranging from the nano-to macro-sizes, depending on the substrate [12,15,16].…”

“…In a previous investigation, a specific nitrogen doping method led to a GUITAR variant with a 0.9 % total nitrogen atomic abundance giving fractions of 0 % graphitic N, 46.0 % pyridinic, 41.3 % pyrrolic, and 12.4 % N-oxide. This electrocatalyst, N(py)-GUITAR, proved to be durable and efficient for the 4etransfer ORR to H 2 O [15]. An alternative doping method produced a nitrogen-doped pseudo-graphite which contains 9.7 % N [13].…”