Anchoring Mo single atoms/clusters and N on edge-rich nanoporous holey graphene as bifunctional air electrode in Zn−air batteries

Materials co-design of the single-atom catalytic centers and the supports can push the limits of the emerging wearable metal-air batteries. The metal single-atom catalysts are required to be bifunctional with high efficient electrocatalytic activities for both oxygen reduction and evolution reactions (ORR and OER), and preferably non-noble. The supports, on the other hand, in addition to the requirements of being free-standing, flexible and porous, are required to strongly interact with the metal species to prevent their aggregation. However, satisfying these requirements simultaneously is yet challenging. Here, a free-standing 3D nanoporous holey graphene with both N and single-atom Mo dopants is prepared. The nanoholes are created by chemical vapor deposition method on nanoporous NiMo alloy templates with their surface decorated with catalytically inert SiO2 nanoparticles. The edge-rich graphene induced by the nanoholes facilitates the doping of pyridinic N and single-atom Mo in the fringe near the edges. The resulting N and Mo co-doped nanoporous holey graphene exhibits high bifunctional ORR and OER catalytic activities in alkaline electrolytes. The synergetic effects between N and Mo dopants are also revealed by density functional theory calculations. When incorporated in a solid-state zinc-air battery, the battery is bendable and can be continuously discharged/charged for 88 h with a high power density of 83 mW cm−2. This work provides an efficient route to design metal single atom/cluster doped 3D freestanding nanoporous graphene as flexible electrodes.