Abstract
The rational design and preparation of hierarchically porous carbons feature high on the wish list of academia and industry alike. However, creating interconnected pores of distinct dimensions is no easy task. Starting from the precursor design, we present a novel synthesis strategy of porous carbons that much enhances the pore interconnectivity. The 500 °C pyrolysis of chelated Mg and Fe nitrilotriacetates creates Fe-doped MgO template, sizing 50–400 nm. While embedded in the carbon matrix, these pyrolysis-generated templates undergo an additional phase transformation at the sequential 900 °C pyrolysis, exsolving well-dispersed smaller Fe nanoparticles, typically sizing 5–45 nm, on the MgO surface. This offers a contiguous network of dual templates for meso- and macropores. A simple acid washing yields a hierarchically porous, N-doped carbon with a high specific surface area of 1560 m2 g−1 and a high mesopore volume of 1.9 cm3 g−1. This carbon exhibits a half-wave potential of 0.77 V vs. RHE in the oxygen reduction reaction at pH 13. Besides, it also renders a specific capacitance of 321 F g−1 at 5 mV s−1 during the capacitor measurement.
Highlights
Functional materials are crucial for the advancement of science and technology, shaping our modern society
Where J is the measured current density, JK is the kinetic current density, u is the rotating disc electrode (RDE) rotation rate, and B is given by: B 1⁄4 0:2nFCOD2O=3nÀ1=6 where 0.2 is the arithmetic correction factor for u in rpm, n is the number of electrons transferred per mol, F is Faraday's constant, CO is the concentration of dissolved O2 (1.2 mmol mlÀ1 at 25 C in 0.1 M KOH), DO is the diffusion coefficient of O2 (1.9 Â 10À5 cm2 sÀ1 at 25 C in 0.1 M KOH), and y is the kinematic viscosity of the 0.1 M KOH electrolyte at 25 C (0.01 cm2/s)
The precursor was prepared following our hydrothermal treatment method of nitrilotriacetic acid mixed with Mg and Fe salts of a 6:1 M ratio (FeMg-NTA) [23]
Summary
Functional materials are crucial for the advancement of science and technology, shaping our modern society. To generate hierarchical porosity and precisely manipulate the pore size, templates of different dimensions must be added to the carbon precursor. It doesn't always guarantee a network with “all-connected-pores”. Inspired by the recent studies on nanoparticle exsolution from perovskite oxides [19,20], we demonstrate here a rational yet facile approach for preparing HPCs. Aiming at increasing the electrochemical performances of the carbon, we promote the mesomacropore interconnectivity using a novel “exsolution” templating method. Aiming at increasing the electrochemical performances of the carbon, we promote the mesomacropore interconnectivity using a novel “exsolution” templating method In this optimized hard-templating approach, the mesopore-template was exsolved from the previously formed macropore-template, naturally creating a connected network of template with dual dimensions. The composition, porous topology and the electrocatalytic performances of the HPCs are discussed
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