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

The electrochemical soluble oxynitrides (NO x –, mainly NO3 – and NO2 –) reduction to synthesize ammonia (NH3) is a sustainable alternative to the energy- and CO2-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 NH3 production yield and selectivity, making the high-performance electrocatalysts urgently needed in driving selective NO x –-to-NH3 conversion. Here, we developed an easily enriched electroactive microorganism biocatalyst in the environment and achieved a NH3 selectivity of 96%. To improve the universality of the high selectivity, we investigated the electron allocation and microbial response mechanisms at different NO2 – concentrations of the biocatalysts. The balance of electron flow in biocatalysts between electricity generation and NH3 synthesis from NO2 – is an essential basis for achieving highly selective NH3 synthesis. Transcriptomics further revealed that NrfAH of Geobacter captured electrons to support high NH3 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 NH3 selectivity enhancement.