Hefei National Laboratory for Physical Sciences at Microscale, Collaborative Innovation Center of Chemistry for Energy Materials, University of Science and Technology of China, Hefei, Anhui 230026, China.
Hefei Science Center of CAS, Hefei, Anhui 230061, China.
Nature. 2016 Jan 7;529(7584):68-71. doi: 10.1038/nature16455.
Electroreduction of CO2 into useful fuels, especially if driven by renewable energy, represents a potentially 'clean' strategy for replacing fossil feedstocks and dealing with increasing CO2 emissions and their adverse effects on climate. The critical bottleneck lies in activating CO2 into the CO2(•-) radical anion or other intermediates that can be converted further, as the activation usually requires impractically high overpotentials. Recently, electrocatalysts based on oxide-derived metal nanostructures have been shown to enable CO2 reduction at low overpotentials. However, it remains unclear how the electrocatalytic activity of these metals is influenced by their native oxides, mainly because microstructural features such as interfaces and defects influence CO2 reduction activity yet are difficult to control. To evaluate the role of the two different catalytic sites, here we fabricate two kinds of four-atom-thick layers: pure cobalt metal, and co-existing domains of cobalt metal and cobalt oxide. Cobalt mainly produces formate (HCOO(-)) during CO2 electroreduction; we find that surface cobalt atoms of the atomically thin layers have higher intrinsic activity and selectivity towards formate production, at lower overpotentials, than do surface cobalt atoms on bulk samples. Partial oxidation of the atomic layers further increases their intrinsic activity, allowing us to realize stable current densities of about 10 milliamperes per square centimetre over 40 hours, with approximately 90 per cent formate selectivity at an overpotential of only 0.24 volts, which outperforms previously reported metal or metal oxide electrodes evaluated under comparable conditions. The correct morphology and oxidation state can thus transform a material from one considered nearly non-catalytic for the CO2 electroreduction reaction into an active catalyst. These findings point to new opportunities for manipulating and improving the CO2 electroreduction properties of metal systems, especially once the influence of both the atomic-scale structure and the presence of oxide are mechanistically better understood.
将二氧化碳电化学还原为有用燃料，特别是如果由可再生能源驱动，代表了一种潜在的“清洁”策略，可以替代化石原料，并应对日益增加的二氧化碳排放及其对气候的不利影响。关键的瓶颈在于将二氧化碳激活为二氧化碳（•-）自由基阴离子或其他可以进一步转化的中间产物，因为这种激活通常需要不切实际的高过电位。最近，基于氧化物衍生的金属纳米结构的电催化剂已被证明可以在低过电位下实现二氧化碳还原。然而，这些金属的电催化活性如何受到其本征氧化物的影响仍不清楚，主要是因为界面和缺陷等微观结构特征会影响二氧化碳还原活性，但却难以控制。为了评估这两种不同催化位点的作用，我们在这里制备了两种四原子厚的层：纯钴金属和共存的钴金属和钴氧化物域。在二氧化碳电化学还原过程中，钴主要产生甲酸盐（HCOO（-））；我们发现，原子层表面的钴原子在较低的过电位下，对甲酸盐生成具有更高的本征活性和选择性，而块状样品表面的钴原子则不然。原子层的部分氧化进一步提高了它们的本征活性，使我们能够在 40 小时内实现约 10 毫安每平方厘米的稳定电流密度，在仅 0.24 伏的过电位下，甲酸盐的选择性约为 90%，优于以前在可比条件下评估的金属或金属氧化物电极。因此，正确的形态和氧化态可以使一种材料从一种被认为几乎对二氧化碳电还原反应没有催化活性的材料转变为一种活性催化剂。这些发现为操纵和改善金属系统的二氧化碳电还原性能提供了新的机会，特别是一旦对原子级结构和氧化物存在的影响在机制上有了更好的理解。
