Methanogens are putatively ancestral autotrophs that reduce CO2 with H2 to form biomass using a membrane-bound, proton-motive Fe(Ni)S protein called the energy-converting hydrogenase (Ech). At the origin of life, geologically sustained H+ gradients across inorganic barriers containing Fe(Ni)S minerals could theoretically have driven CO2 reduction by H2 through vectorial chemistry in a similar way to Ech. pH modulation of the redox potentials of H2, CO2 and Fe(Ni)S minerals could in principle enable an otherwise endergonic reaction. Here, we analyse whether vectorial electrochemistry can facilitate the reduction of CO2 by H2 under alkaline hydrothermal conditions using a microfluidic reactor. We present pilot data showing that steep pH gradients of approximately 5 pH units can be sustained over greater than 5 h across Fe(Ni)S barriers, with H+-flux across the barrier about two million-fold faster than OH--flux. This high flux produces a calculated 3-pH unit-gradient (equating to 180 mV) across single approximately 25-nm Fe(Ni)S nanocrystals, which is close to that required to reduce CO2. However, the poor solubility of H2 at atmospheric pressure limits CO2 reduction by H2, explaining why organic synthesis has so far proved elusive in our reactor. Higher H2 concentration will be needed in future to facilitate CO2 reduction through prebiotic vectorial electrochemistry.

中文翻译：

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H2 通过生命起源前矢量电化学还原 CO2 的可能机制。

产甲烷菌被认为是祖先的自养生物，它们利用膜结合的质子动力 Fe(Ni)S 蛋白（称为能量转换氢化酶 (Ech)）用 H2 还原 CO2，形成生物质。在生命起源时，地质上持续的 H+ 梯度穿过含有 Fe(Ni)S 矿物的无机屏障，理论上可以通过矢量化学以与 Ech 类似的方式驱动 CO2 还原。H2、CO2 和 Fe(Ni)S 矿物的氧化还原电位的 pH 调节原则上可以实现吸能反应。在这里，我们使用微流控反应器分析了矢量电化学是否可以促进碱性水热条件下 H2 还原 CO2。我们提供的试点数据显示，约 5 个 pH 单位的陡峭 pH 梯度可以在跨越 Fe(Ni)S 屏障的情况下持续超过 5 小时，穿过屏障的 H+ 通量比 OH- 通量快约 200 万倍。这种高通量在单个约 25 nm Fe(Ni)S 纳米晶体上产生计算出的 3-pH 单位梯度（相当于 180 mV），这接近于减少 CO2 所需的梯度。然而，H2在大气压下的溶解度较差，限制了H2对CO2的还原，这解释了为什么有机合成迄今为止在我们的反应器中难以实现。未来将需要更高的氢气浓度，以通过益生元矢量电化学促进二氧化碳还原。