Abstract
The direct synthesis of hydrogen peroxide using sustainable energy and molecular oxygen is a promising alternative approach to the conventional batch synthesis. Here we present a manganese and nitrogen co-doped carbon material which catalyzes the selective reduction of dioxygen in an acidic environment to hydrogen peroxide. The onset potential is close to 0.7 V, with >98% H2O2 selectivity in the range of 0.7–0.5 V vs RHE. This is the highest reported to date, outperforming many bimetallic noble metal catalysts. Besides, this doped carbon material is hierarchically porous, featuring both a large mesopore volume (4.54 mL g−1) and a high specific surface area (1333 m2 g−1). This enables the effective adsorption of bulky organics such as methylene blue (385 mg g−1). Combined with the formation of hydroxyl radicals during electrochemical H2O2 generation, this material also enables the efficient electrochemical degradation of methylene blue, as evidenced by in situ UV–vis spectrometry.
Highlights
Industrial wastewater often contains toxic organic pollutants
The oxygen reduction reaction (ORR) takes advantage of the readily-available oxygen dissolved in the water to produce hydrogen peroxide
By comparing the high-resolution transmission electron microscopy (HRTEM) images in Fig. 2e and f, we confirmed that these mesopores were templated by the MnO nanoparticles
Summary
Industrial wastewater often contains toxic organic pollutants. Traditional water treatment traps these contaminants in the sludge, incurring a large environmental footprint [1e4]. Because the reactive hydroxyl radicals are short-lived, the organic contaminants must be adsorbed and held at the electrode in close proximity to the radical-generating sites This means that the H2O2-formation catalyst should be a porous material, allowing the capture of the organic pollutants. Based on our recent research into nitrogen-doped carbon (NeC) catalysts, we hypothesized that an active and selective catalyst for reducing O2 to H2O2 with a high pore volume would both capture bulky organic pollutants from water and catalyze their degradation. We report a facile synthesis of hierarchically Mn and N codoped carbon nanorods (MneNeC) starting from nitrilotriacetic acid This material, with its large pore volume of 4.54 cm gÀ1 and a high specific surface area of 1333 m2 gÀ1, can adsorb 385 mg gÀ1 of methylene blue (MB, a dye with many industrial applications) [33e37]. This combined adsorption and electrocatalytic activity opens new opportunities for wastewater treatment as well as for electrocatalysis applications
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