Ultrapure Graphene Is a Poor Electrocatalyst: Definitive Proof of the Key Role of Metallic Impurities in Graphene-Based Electrocatalysis

Abstract

Graphene and its derivatives have been reported in many articles as “metal-free” carbon electrocatalytic materials. Its synthesis procedures are generally based on the chemical oxidation of graphite and subsequent thermal or chemical reduction. Because graphene oxide has a large surface area and typically contains a variety of oxygen functionalities, metallic ions (impurities) from reaction mixtures can be adsorbed on its surface. These impurities can significantly enhance the electrocatalytic activity and thus lead to data misinterpretation; such impure samples are referred to as “metal-free” catalysts. In this paper, we report the synthesis of impurity-free graphene, which is compared with graphene prepared by standard methods based on the thermal and chemical reduction of two graphene oxides. Detailed analysis of graphene prepared by standard methods shows a direct relation between metallic impurities and the electrocatalytic activity of graphene. In contrast, impurity-free graphene exhibits poor electrocatalytic activity.

Synthesis of Highly Crystalline Graphite from Spontaneous Ignition of In Situ Derived Acetylene and Chlorine at Ambient Conditions

“…Specifically, iron impurities are very common in synthetic graphite [19]. Furthermore, metallic impurities are sometimes advantageous in electroanalysis, since they provide significantly larger voltammetric currents and enhance electrocatalytic activity [20,21]. Finally, the solid had the lustrous grey appearance of graphite ( Figure S6), while its thermal decomposition in air occurred at >600 • C ( Figure S7).…”

Synergistically Coupling Black Phosphorus Quantum Dots with MnO2 Nanosheets for Efficient Electrochemical Nitrogen Reduction Under Ambient Conditions

“…Unfortunately, the electrocatalytic performance of pure graphene without metallic impurities is inappreciable, while MXene nanosheets equipped with moderate activity suffer complicated synthesis procedures and intense tendency of being oxidized. [ 26–28 ] Therefore, searching for a high‐activity 2D substrate is of paramount importance. Mn element is proposed to dramatically facilitate the catalytic performance of nitrogenanses in extracts from the photosynthetic bacterium Rhodospirillum rubrum .…”

Stable Confinement of Black Phosphorus Quantum Dots on Black Tin Oxide Nanotubes: A Robust, Double‐Active Electrocatalyst toward Efficient Nitrogen Fixation

“…Previously, we employed reduced graphene oxide (RGO) as a matrix to support BP QDs, thereby preventing their agglomeration and enhancing their conductivity . Unfortunately, RGO was electrocatalytically inert, and its presence as an inactive component would impose an adverse effect on the ammonia yield per unit mass …”