Strategic Structure Tuning of Yolk-Shell Microcages for Efficient Nitrogen Fixation

Graphical In the bag : An optimized one-step pyrolysis strategy is used to design yolk–shell microcages (YS Co@C/BLCNTs), consisting of Co nanocrystals encapsulated in N-doped carbon framework and bridged by bamboo-like carbon nanotubes (BLCNTs).The yolk–shell microcage catalyst integrates the advantages of “micro-bag” and “cage effect” to realize effective nitrogen fixation. The electrocatalytic nitrogen reduction reaction (ENRR) under ambient conditions is considered as a promising process to produce ammonia. Towards highly efficient catalysts, here an optimized one-step pyrolysis strategy was tailored to design yolk–shell microcages (YS Co@C/BLCNTs), consisting of Co nanocrystals encapsulated in N-doped carbon framework and bridged by bamboo-like carbon nanotubes (BLCNTs). The cavity created between yolk and shell not only served as a “micro-bag” to store the reactant N 2 and enhance its dissolution, but also induced a “cage effect” to confine the diffusion of reaction intermediate, hence making the reaction proceed in the direction of producing NH 3 . This catalyst displayed excellent catalytic activities for ENRR: a high NH 3 yield of 12.87 μg mg cat −1 h −1 at a high faradaic efficiency of 20.7 % at −0.45 V (vs. reversible hydrogen electrode, RHE). After 5 cycles of consecutive ENRR process, the NH 3 yield rate was 11.29 μg mg cat −1 h −1 , indicating the excellent electrocatalytic stability. These results provide a structural engineering for ENRR catalyst with doped N, cooperating with non-precious metal to activate the inert triple bond of N 2 and achieve NH 3 fixation.