Shrinking Electron Transfer Barrier between Carbon Skeleton and Oxygen to Enhance Oxygen Reduction Reaction Through Constructing Locally Ordered Graphene Microcrystals

Adjustment of electronic structure in carbon skeleton has a major impact on the performance of carbon material for oxygen reduction reaction (ORR). Decreasing work function of carbon skeleton is one of the significant research branches for the development of carbonaceous catalysts. Herein, utilizing the structural features of graphene microcrystals (“house of cards” model), the work function of carbon skeleton is reduced after inducing the conversion of bridging sp3-C to bridging sp2-C (ratio of sp2-C to sp3-C increases from 3.87 to 7.13). The increasing contact potential difference (from 17 to 43 mV) reveals the decline of work function. The lower work function of locally ordered microarchitectures has been proved to decrease the first electron transfer barrier from catalyst surface to π* orbit of O2 in outer-Helmholtz plane. After rearrangement of bridging carbon atoms, the kinetic current density and half-wave potential can increase from 4.1 mA cm−2 and 0.846 V to 5.5 mA cm−2 and 0.874 V, respectively. Furthermore, the locally ordered microarchitectures exhibit outstanding discharge performance in Zn-air battery device (discharge voltage platform increases from 1.19 to 1.31 V). The locally ordered elementary microcrystals in hard carbon system provide a new direction of structure design for ORR at the atomic level