Hydrogen is a promising fuel in a carbon-neutral economy, and many efforts are currently undertaken to produce hydrogen. One of the challenges is to store and transport the highly explosive gas in a safe and easy way. One option that is intensively analyzed by chemists and biologists is the conversion of hydrogen and CO₂ to formic acid, the liquid organic hydrogen carrier. Here, we demonstrate for the first time that a bio-based system, using Acetobacterium woodii as the biocatalyst, allows multiple cycles of bi-directional hydrogenation of CO₂ to formic acid in one bioreactor. The process was kept running over 2 weeks producing and oxidizing 330 mM formic acid in total. Unwanted side-product formation of acetic acid was prevented through metabolic engineering of the organism. The demonstrated process design can be considered as a future “bio-battery” for the reversible storage of electrons in the form of H₂ in formic acid, a versatile compound.

在碳中和经济中，氢是一种很有前途的燃料，目前正在努力生产氢。挑战之一是以安全和简单的方式储存和运输高爆炸性气体。化学家和生物学家深入分析的一种选择是将氢和 CO ₂转化为甲酸，即液态有机氢载体。在这里，我们首次展示了一个以木醋杆菌为生物催化剂的生物基系统，可以实现多个循环的 CO ₂双向加氢。在一个生物反应器中生成甲酸。该过程持续运行 2 周以上，总共产生和氧化 330 mM 甲酸。通过生物体的代谢工程防止了乙酸的不需要的副产物形成。所展示的工艺设计可以被视为未来的“生物电池”，用于在甲酸（一种多功能化合物）中以 H _{2的形式可逆存储电子。}