Identifying Activity and Selectivity Trends for the Electrosynthesis of Hydrogen Peroxide via Oxygen Reduction on Nickel–Nitrogen–Carbon Catalysts

Abstract

The electrocatalytic production of hydrogen peroxide (H 2 O 2 ) through the two-electron oxygen reduction reaction (ORR) requires costeffective catalysts with high selectivity, activity, and stability. Herein we report the synthesis and electrocatalytic assessment of nickel−nitrogen−carbon (Ni−N−C) electrocatalysts to gain insight into ORR activity and selectivity toward the production of H 2 O 2 . The activity and selectivity of the catalysts depended on the amount of nickel added during synthesis as well as the pH of the electrolyte. The materials were found to be heterogeneous in nature, consisting of nitrogen-doped carbon structures containing Ni species, including Ni 3 S 2 and covered metallic Ni particles. The presence of Ni during synthesis was imperative for the ORR performance in acidic electrolytes but had minimal impact on the performance in alkaline electrolytes. By experimentally demonstrating that Ni 3 S 2 , metallic Ni, and N-doped carbon species were not the source of activity, we postulate that atomically dispersed Ni−N x /C sites are responsible for the ORR performance in acidic electrolytes, with an activity of −0.3 mA cm −2 and a H 2 O 2 selectivity of 43% measured for the best Ni−N−C catalyst at 0.5 V vs RHE. This work highlights the potential and generates scientific insight into Ni− N−C catalysts to guide the design of improved performance metal−nitrogen−carbon catalysts based on inexpensive precursors and simplistic syntheses.

Chemical Structure and Distribution in Nickel–Nitrogen–Carbon Catalysts for CO2 Electroreduction Identified by Scanning Transmission X-ray Microscopy

“…Our previous research showed that the Ni–N–C samples (Ni–N–C-high, Ni–N–C-low) used in this study consist of Ni-containing particles distributed throughout a nitrogen-doped carbonaceous matrix, with an increasing quantity of particles observed when higher amounts of nickel chloride were used in the synthesis. The presence of Ni-based particles following acid leaching is likely due to two reasons.…”

“…The synthesis of the Ni–N–C catalysts has been reported previously . Briefly, the Ni–N–C catalysts were prepared by mixing aniline (1 mL, Sigma-Aldrich), cyanamide (2 g, Sigma-Aldrich), and nickel chloride hexahydrate (NiCl 2 ·6H 2 O, Sigma-Aldrich) in a 1.5 M HCl solution (200 mL, ACS reagent).…”

“…The samples studied were a series of pyrolyzed, polymerderived Ni−N−C catalysts that were investigated previously for their oxygen reduction reaction performance and chemical composition. 42 a powerful tool for characterization of electrocatalyst materials and is an essential step toward in situ electrochemical STXM measurements 43 that our team is currently performing.…”

Effect of Nitrogen Species in Graphite Carbon Nitride on Hydrogen Peroxide Production

“…[13] Shahcheraghi et al prepared electrocatalysts by dispersing nickel atoms in a carbon-nitrogen network (NiNC), and achieved the selectivity of 43% at 0.5 V versus RHE. [14] Graphitic carbon nitride (g-C 3 N 4 ) has received attention as a nonmetallic catalyst due to its rich electronic structure, good physical and chemical stability. [15] Recent studies have shown that g-C 3 N 4 can be used as an ideal platform for regulating the electronic structure and geometric structure for catalysis.…”

“…[ 13 ] Shahcheraghi et al prepared electrocatalysts by dispersing nickel atoms in a carbon‐nitrogen network (NiNC), and achieved the selectivity of 43% at 0.5 V versus RHE. [ 14 ]…”