High-Selective Microbial Electrocatalytic Ammonia Synthesis from Nitrite: Unlocking Electron Allocation Mechanisms in Controllable Biocatalysts

Abstract

The electrochemical soluble oxynitrides (NO x − , mainly NO 3 − and NO 2 − ) reduction to synthesize ammonia (NH 3 ) is a sustainable alternative to the energy-and CO 2 -intensive Haber-Bosch process, providing a promising avenue to address the challenges of environmental nitrogen management and high-value "zero-carbon" fuel production. However, the inevitable byproduct formation during the complicated proton-coupled multielectron transfer process severely limits the NH 3 production yield and selectivity, making the high-performance electrocatalysts urgently needed in driving selective NO x − -to-NH 3 conversion. Here, we developed an easily enriched electroactive microorganism biocatalyst in the environment and achieved a NH 3 selectivity of 96%. To improve the universality of the high selectivity, we investigated the electron allocation and microbial response mechanisms at different NO 2 − concentrations of the biocatalysts. The balance of electron flow in biocatalysts between electricity generation and NH 3 synthesis from NO 2 − is an essential basis for achieving highly selective NH 3 synthesis. Transcriptomics further revealed that NrfAH of Geobacter captured electrons to support high NH 3 selectivity. Therefore, this study provides theoretical support for understanding the biocatalyst function in electrochemical NO x − reduction and offers a novel strategy for the enhancement of NH 3 selectivity enhancement.