Fabrication of Mn,N‐Codoped Carbon Electrocatalysts from a Cationic Cd(II)‐based MOF Involving Anion‐exchange with MnO₄⁻ Anions

Abstract

Mn and N-codoped carbon materials (MnÀ NÀ C) have recently aroused enormous interest owing to their unique advantages over Fe-NÀ C counterparts. MnÀ NÀ C electroactive materials have been conveniently fabricated from a cationic Cd(II)-based MOF (CdÀ TTPBA-4(TTPBA-4 = N 1 ,N 1 ,N 4 ,N 4-tetrakis(4-(4H-1,2,4-triazol-4-yl)phenyl)benzene-1,4-di-amine) which can effectively and controllably achieve the Mn-doping through anion-exchange between the exterior MnO 4 À anions and its exchangeable ClO 4 À anions. The anion-exchanged materials of MnO 4 À @CdÀ TTPBA-4 were pyrolyzed at 1000°C followed by acid-washing and second heat-treatment to give MnÀ NÀ C electroactive materials with promising oxygen reduction activity. In the alkaline electrolyte, the optimal MnÀ NÀ C material exhibits an outstanding oxygen reduction activity with the onset potential of 0.93 V (vs RHE) and half-wave potential of 0.82 V (vs RHE), together with a good long-term stability.

Metal–Organic-Framework-Derived Atomically Dispersed Mn–N–C Electrocatalysts Boosting Oxygen Reduction Modulated by Anion Exchange of Permanganate

“…The BET surface area of Mn–N–C-0.9-1000-AT attains a value of 1132.8 m 2 /g, which is nearly contributed by its dominant micropores (889.1 m 2 /g). The high microporosity of Mn–N–C-0.9-1000-AT is assumed to be from evaporation of Cd atoms (bp 705 °C) during the pyrolysis, which is beneficial for hosting dense M–N x active sites. − In sharp contrast with the Mn–N–C-0.9-1000-AT in this work, our previously reported Mn–N–C material (namely, Mn–N–C-1000-0.6-AT) derived from MnO 4 – @ Cd-TTPBA-4 exhibits a very small surface area (216.6 m 2 /g) but abundant mesopores . Apparently, the difference could be largely caused by the different MOF structures hosting MnO 4 – .…”

“…49−51 In sharp contrast with the Mn−N−C-0.9-1000-AT in this work, our previously reported Mn−N−C material (namely, Mn−N− C-1000-0.6-AT) derived from MnO 4 − @ Cd-TTPBA-4 exhibits a very small surface area (216.6 m 2 /g) but abundant mesopores. 44 Apparently, the difference could be largely caused by the different MOF structures hosting MnO 4 − . The Cd-MOF in this work that is exclusively based on Cd−N coordination bonds exhibits better thermal stability than Cd-TTPBA-4 MOF built with both Cd−N and Cd−O bonds, which could inhibit quick framework collapse during the pyrolysis, thus maintaining the high microporosity of MOFs.…”

“…Afterward, we composed Mn−N−C electrocatalysts by use of a positively charged Cd(II)-based MOF precursor (namely, Cd-TTPBA-4), which can finely control Mn doping through anion exchange. 44 Despite the optimal Mn−N−C catalyst in that work being still inferior to the reference Pt/C, the anionexchange method has demonstrated uniqueness in tuning the metal-doping content and then optimizing the oxygen reduction activity of M−N−C materials. 45 As well demonstrated in the literature, MOF precursors have a crucial impact on the electrocatalytic performances of their derived M−N−C materials since their different compositions, structures, and morphologies directly govern the nature of the active sites and carbon matrix of M−N−C electrocatalysts.…”

“…Different from the Cd-TTPBA-4 described in our previous work, the Cd-MOF in this work, built by pure Cd–N coordination bonds, exhibits a one-dimensional channel accommodating disordered NO 3 – anions that can exchange with MnO 4 – anions . The better chemical and thermal stability of Cd-MOF than those of Cd-TTPA-4 would prevent quick framework collapse during pyrolysis, which would lead to fewer exposed active sites and a small surface area . The three-dimensional order of Cd-MOF coupled with accurate modulation of the Mn content based on anion exchange offers a great advantage to improve the ORR kinetics of Mn–N–C electrocatalysts.…”

Cationic metal–organic frameworks constructed from a trigonal imidazole-containing ligand for the removal of Cr2O72− in water

“…Therefore, the synthesis of cationic MOFs and their application in the treatment of wastewater containing anionic pollutants has aroused special attention recently. [42][43][44][45][46][47][48][49][50] Additionally, as one of the most widely used organic struts in the construction of MOFs, neutral N-donor ligands have better access to cationic MOFs upon coordination with cationic metal centers in comparison with another popular ligand type, namely carboxylate ligands. For example, Li and coworkers utilized 4,4 0 -bis(1,2,4triazole) (btr) and Ag(I) to fabricate a novel cationic MOF with distorted octahedral and tetrahedral cages and applied it in the capture of Cr 2 O 7…”