The metal-nitrogen-carbon (M-N-C) type oxygen reduction reaction (ORR) catalysts are promising for hydroxide exchange membrane fuel cells, but catalysts with further improved performance are challenging. Here, we report the efficient improvement of the ORR activity of M-N-C catalysts by employing highly polarizable metal cation Ag + . Ag, Fe single atomic sites embedded in concave nitrogen doped carbon (Ag 1 Fe 1 /CNC) is successfully synthesized and shows high performance towards ORR, indicating by both the ultra-high half-wave potential of 0.917 V and membrane electrolyte assembly performance of peak power density up to 1.26 W cm −2 . The binding energy of the ORR intermediates on the highly polarizable Ag site in Ag 1 Fe 1 /CNC was significantly tuned by the adjacent Fe site by more than 0.2 eV, and thus leading to a low theoretical ORR overpotential of only 0.398 V. The employment of the highly polarizable metal cation brings a novel and efficient approach to construct highly active catalysts.
Xu Hu,Ling-Yu Dong,Yong-Qi Ren,Wen-Cui Li,Martin Oschatz,Guang-Ping Hao,An-Hui Lu
The efficient utilization of active centers for the emerging class of metal (M) and nitrogen (N) co-doped carbon (M–N–C) catalysts remains a research hotspot for electrochemical synthesis such as the reduction reactions of CO2, O2, N2, or functional groups in organic molecules. However, keeping sufficient accessibility to these active centers upon thermal treatment at high temperatures can be challenging due to possible nanopore blocking issues. To tackle this limitation, this work presents a precise surface modulation approach based on a kind of porous carbon support with an ultrapolar surface, over which the unusual enhancement of nanopore accessibility and metal utilization is achieved. The strategy is well applicable to transition metals, precious metals, and rare earth metals. Experimental evidence revealed that the ultrapolar pore walls can be spontaneously wetted by hydrated metal ions. The unprecedented wettability ensured a unique metal-support interaction, which not only warrants the anchoring metal species in a dispersed manner but also induces the development of transport nanopores by dynamical etching of the polar carbon walls during thermal treatment. By this way, this strategy addresses the trade-off issue between metal utilization efficiency and accessibility to the active centers for the M–N–C type catalysts.
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