Nickel nanoparticle-embedded N-doped carbon catalysts formed by MOF derivatives for the oxygen evolution reaction

Abstract

MOF-derived materials have recently attracted considerable interest as alternatives to noble-metal electrocatalysts. Herein, the rational design and synthesis of nickel nanoparticle-embedded N-doped carbon catalysts (Ni-N/C) from Ni-MOF and melamine by pyrolysis is reported. MOF-derived Ni-N/C electrocatalysts consisting of homogeneously distributed nickel nanoparticles encapsulated by N-doped carbon rings exhibit higher electrocatalytic activities for the oxygen evolution reaction (OER). In order to obtain optimized preparation conditions of MOF-derived Ni-N/C materials for the OER, the overpotential of the Ni-MOF derived materials was measured by linear sweep voltammetry (LSV). The results showed that the best synthesis conditions of nickel nanoparticle-embedded N-doped carbon catalysts were as follows: Ni-MOF with the molar ratio of Ni²⁺ to pyridine-2,5-dicarboxylic acid of 2 : 5 was used as the precursor, the mass ratio of melamine to Ni-MOF was 2 : 2, and the carbonization temperature was 900 °C. The oxygen evolution overpotential of Ni-N/C (labeled as 5-Ni-N/C (2 : 2)-900) was 394 mV. The ECSA value of 5-Ni-N/C (2 : 2)-900 was 254.25 cm² obtained from cyclic voltammetry (CV). The R_ct value of 5-Ni-N/C (2 : 2)-900 was 7.20 Ω. More importantly, the stability test (i–t curve) proved that the MOF derived materials exhibited good stability. The remarkable electrochemical properties are mainly attributed to the synergistic effect from isolated single atoms uniformly dispersed over the carrier and a large number of bond structures as well as coordination sites, which can not only maximize the efficiency of metal atoms, but also firmly anchor metal atoms, and effectively solve the problem that metal atoms are easy to coalesce due to high surface free energy. The Ni-N/C derivative has excellent catalytic performance in oxygen evolution reactions and is the most promising non-noble metal catalyst to replace the noble metal catalysts.