Coupling the Atomically Dispersed Fe-N3 Sites with Sub-5 nm Pd Nanocrystals Confined in N-Doped Carbon Nanobelts to Boost the Oxygen Reduction for Microbial Fuel Cells

Both the monodispersed Pd/C (2-5 nm) and Fe-NC single atoms (SAs) are promising non-Pt catalysts for oxygen reduction reaction (ORR), which belongs to precious metal and nonprecious metal camps, respectively. However, the poles apart of sub-5 nm Pd/C and Fe-NC SAs in synthesis and thermostability leave the challenge to integrate them together in one system. Herein, a 1-naphthylamine protected pyrolysis mechanism is devised to couple the atomically dispersed Fe sites with sub-5 nm Pd nanocrystals embedded in N-doped carbon nanobelts (FeN3-Pd@NC NBs). The FeN3 SAs represent the minimal surface blockage to tune the electronic structure of Pd, while the carbon frameworks are born with ultrathin, porous, and N-doped feature's. As inspired, the FeN3-Pd@NC NBs exhibit outstanding activity (E-1/2 = 0.926 V) and durability (2 mV decay in E-1/2 after 2000 cycles) for ORR, as well as achieving a maximum power density of 831.2 mW cm(-2) in a microbial fuel cell operated for over 100 d. Density functional theory calculation reveals that the FeN3 SAs can shift the density of states of Pd toward the Fermi level, and their coupling can decrease the limiting reaction barrier with a value of -0.62 eV, thus greatly accelerating the ORR kinetics.