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Construction of a cobalt-embedded nitrogen-doped carbon material with the desired porosity derived from the confined growth of MOFs within graphene aerogels as a superior catalyst towards HER and ORR

Zhu, Zhen, Yang, Yan, Guan, Yue, Xue, Juanhong, Cui, Lili
Journal of materials chemistry A 2016 v.4 no.40 pp. 15536-15545
aerogels, catalysts, cobalt, coordination polymers, electrochemistry, energy, fuel cells, graphene, hydrogen production, macropores, micropores, pH, porosity, renewable energy sources, sulfuric acid, surface area, synergism
Hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) are vital in renewable energy technologies, such as water splitting and fuel cells. Nevertheless, increasing efforts have been paid to develop non-precious metal catalysts as alternatives to noble metal catalysts for HER and ORR. However, how to rationally design and construct an advantageous catalyst is still challenging. Here, a novel cobalt-embedded in nitrogen-doped graphene aerogel (Co–N–GA) catalyst is firstly rationally designed and synthesized by employing a facile strategy of implementing the confined growth of metal organic frameworks (MOFs) within graphene aerogels (GAs). It is worth noting that the Co–N–GA exhibits hierarchical porosity involving micropores, mesopores and macropores, as well as a high surface area (466.6 m² g⁻¹). More importantly, benefiting from the synergetic effect of hierarchical porosity, high surface area, N-doped carbon and the inner Co metal, the catalyst Co–N–GA displays extraordinarily superior activity for both HER at various pH values and ORR along with better stability. Especially for HER, the onset overpotential, overpotentials@10, 100 mA cm⁻² and Tafel slope on the catalyst Co–N–GA in 0.5 M H₂SO₄ are 0 mV, 46 mV, 183 mV and 33 mV dec⁻¹, respectively. Most importantly, these values are much lower than those of almost all prepared noble-metal-free HER catalysts, indicating the excellent activity for HER of our as-prepared catalyst Co–N–GA. Herein, our strategy opens a new platform to construct a variety of hierarchically porous GA-based catalysts that serve as superior electrocatalysts in energy storage and conversion technologies.