CO ₂ reduction driven by a pH gradient

Abstract

Significance Biology is built of organic molecules, which originate primarily from the reduction of CO 2 through several carbon-fixation pathways. Only one of these—the Wood–Ljungdahl acetyl-CoA pathway—is energetically profitable overall and present in both Archaea and Bacteria, making it relevant to studies of the origin of life. We used geologically pertinent, life-like microfluidic pH gradients across freshly deposited Fe(Ni)S precipitates to demonstrate the first step of this pathway: the otherwise unfavorable production of formate (HCOO – ) from CO 2 and H 2 . By separating CO 2 and H 2 into acidic and alkaline conditions—as they would have been in early-Earth alkaline hydrothermal vents—we demonstrate a mild indirect electrochemical mechanism of pH-driven carbon fixation relevant to life’s emergence, industry, and environmental chemistry.