Ligand-exchange-induced child-mother metal-organic frameworks derived a novel heterostructured iron-based carbon for neutral oxygen reduction in microbial fuel cell

Abstract

The slow neutral oxygen reduction reaction (ORR) impedes the efficiency of microbial Fuel Cell (MFC) for pollutants degradation and electricity generation, which requires active electrocatalysts to accelerate electron transfer. Iron-nitrogen-carbons (Fe–N–Cs) derived from Prussian blue analogues (PBAs), acknowledged for low cost and high yield, are generally with unsatisfactory surface structure and low nitrogen/carbon contents, which leads to reduced active sites. To address this issue, herein, an ingenious ligand exchange strategy is proposed for the first time to construct a PBAs-based MOF@MOF precursor (Zn-ZIF-L@Zn–Fe PBA, MOF: metal-organic framework) by utilizing 2D leaf-shaped Zn-based zeolitic imidazolate framework (Zn-ZIF-L) nanoplates to give birth to 3D Zn–Fe PBA nanospheres. Physicochemical and electrochemical results demonstrate that ligand exchange follows diffusion-controlled mechanism and the creatively developed electrocatalyst (C–Zn-ZIF-L@Zn–Fe PBA) with a multi-structure of nanospheres, dense carbon nanotubes and leaf-like carbon nanoplates exhibits remarkable catalytic activity and stability for neutral-pH ORR. The maximum power density of MFC with C–Zn-ZIF-L@Zn–Fe PBA cathode is 2511 ± 69 mW m−2 and chemical oxygen demand (COD) removal efficiency reaches to 90.17%, significantly outperforming the carbonization products of the other two single MOF. For practical application, two MFCs in series can as a power supplier to drive a digital watch for working 24 h constantly.