fig1

Figure 1. Synthesis scheme. (A) FeNC-S-Fe_xC/Fe catalysts. Reproduced with permission from Ref.^[59], © WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 2018.(B) Ir@NBD-C catalysts. Reproduced with permission from Ref.^[63], © WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 2022. (C) Co₂P/CoN-in-NCNTs catalysts. Reproduced with permission from Ref.^[45], © WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 2018.