Department of Chemistry, Stanford University, Stanford 94305, California.
National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley 94720, California.
Nature. 2014 Apr 24;508(7497):504-7. doi: 10.1038/nature13249. Epub 2014 Apr 9.
The electrochemical conversion of CO2 and H2O into liquid fuel is ideal for high-density renewable energy storage and could provide an incentive for CO2 capture. However, efficient electrocatalysts for reducing CO2 and its derivatives into a desirable fuel are not available at present. Although many catalysts can reduce CO2 to carbon monoxide (CO), liquid fuel synthesis requires that CO is reduced further, using H2O as a H(+) source. Copper (Cu) is the only known material with an appreciable CO electroreduction activity, but in bulk form its efficiency and selectivity for liquid fuel are far too low for practical use. In particular, H2O reduction to H2 outcompetes CO reduction on Cu electrodes unless extreme overpotentials are applied, at which point gaseous hydrocarbons are the major CO reduction products. Here we show that nanocrystalline Cu prepared from Cu2O ('oxide-derived Cu') produces multi-carbon oxygenates (ethanol, acetate and n-propanol) with up to 57% Faraday efficiency at modest potentials (-0.25 volts to -0.5 volts versus the reversible hydrogen electrode) in CO-saturated alkaline H2O. By comparison, when prepared by traditional vapour condensation, Cu nanoparticles with an average crystallite size similar to that of oxide-derived copper produce nearly exclusive H2 (96% Faraday efficiency) under identical conditions. Our results demonstrate the ability to change the intrinsic catalytic properties of Cu for this notoriously difficult reaction by growing interconnected nanocrystallites from the constrained environment of an oxide lattice. The selectivity for oxygenates, with ethanol as the major product, demonstrates the feasibility of a two-step conversion of CO2 to liquid fuel that could be powered by renewable electricity.
将 CO2 和 H2O 电化学转化为液体燃料是高密度可再生能源存储的理想选择，并且可以为 CO2 捕获提供动力。然而，目前还没有用于将 CO2 及其衍生物有效还原为理想燃料的高效电催化剂。尽管许多催化剂可以将 CO2 还原为一氧化碳（CO），但液体燃料的合成需要进一步还原 CO，使用 H2O 作为 H(+) 源。铜（Cu）是唯一已知的具有可观 CO 电还原活性的材料，但在块状形式下，其用于液体燃料的效率和选择性对于实际应用来说太低了。特别是，在 Cu 电极上，H2O 还原为 H2 的竞争超过了 CO 的还原，除非施加极高的过电势，此时主要的 CO 还原产物是气态烃。在这里，我们展示了由 Cu2O 制备的纳米晶 Cu（“氧化物衍生的 Cu”）在 CO2 饱和碱性 H2O 中，在适度的电势（相对于可逆氢电极为-0.25 至-0.5 伏特）下，具有高达 57%的法拉第效率，产生多碳含氧物（乙醇、乙酸盐和正丙醇）。相比之下，当通过传统的蒸汽冷凝制备时，具有与氧化物衍生铜相似的平均晶粒尺寸的 Cu 纳米颗粒在相同条件下几乎只产生 H2（96%的法拉第效率）。我们的结果表明，通过从氧化物晶格的受限环境中生长互联的纳米晶，可以改变 Cu 对这种众所周知的困难反应的内在催化性质。对于含氧物的选择性，以乙醇为主要产物，证明了通过可再生电力将 CO2 两步转化为液体燃料的可行性。
