Electrochemical Reduction of Carbon Dioxide

二氧化碳的电化学还原

• 批准号: 2445978
• 金额: --
• 依托单位: University of Liverpool
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2020
• 资助国家: 英国
• 起止时间: 2020 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2445978
• 关键词: Electrochemical; Reduction; Carbon; Dioxide

Society relies heavily on the use of virgin fossil fuels as feedstock for chemical and plastics manufacturing. As pressure to decarbonise builds, this is not possible for all industries, leading to an increasing threat of financial penalties for high CO2 emitters that are unable to completely decarbonise, like cement, steel and glass producers. Electrochemical CO2 reduction provides an opportunity to utilise intermittent renewable energy sources (wind, solar) to drive the conversion of CO2 into useful products. These products range from CO (component of syngas) to sustainable aviation fuel. Electrochemical CO2 reduction is a mature technology, however, due to the requirement for rapid development to achieve Net Zero by 2050, research into the challenges and opportunities for process scale-up has accelerated. In this work, I show the use of a cheap Mn electrocatalyst in two common electrolysers, a flow-cell and a zero-gap cell, designed to achieve higher currents than a typical batch electrochemical experiment. I show that the Mn operates with increased partial current densities for CO (jCO) of 13.7 mA cm-2 than has previously been reported in near-neutral electrolyte in a flow-cell. However, device stability is poor with jCO dropping to <5 mA cm-2 after 5 hours. In basic environments, the Mn catalysts demonstrates low activity with jCO <10 mA cm-2, although in an acidic environment selectivity for CO is good with jCO ~35 mA cm-2. As we move towards industrialisation for decarbonisation processes, it is critical to understand the importance of impure gas feeds on CO2 reduction. Typically, studies have focussed on an ultra-pure CO2 stream as feedstock for electrolysis, however, in reality both flue gas and captured CO2 contain impurities like O2. Therefore, it is imperative to understand the impact of even small concentrations on electrolysis selectivity and devices. Often, if the impact of O2 is explored, device failure mechanisms are not explained, leading to a knowledge gap. Following on from my work using pure CO2, I explore the impact of small concentrations of O2 on both the Mn complex and a simple Au catalyst. I show that the presence of 5% O2 impedes CO2 reduction in acid, and I move on to study Au as a catalyst. I benchmark Au activity in pure CO2 showing high selectivity for CO with jCO ~90 mA cm-2, although when 0.25% O2 is introduced jCO decreased to 80 mA cm-2. Significantly, the introduction of O2 decreases device stability (5 hours to 3 hours operation) due to peroxide formation leading to increased (bi)carbonate formation. I show that providing an acidic environment has a small impact on improving O2-tolerance but sacrifices CO selectivity (45 mA cm-2 to 24 mA cm-2) and cell voltage (2.6 V to 3.4 V). Finally, I screen polymer additives to suppress O2-reduction. I find that by selecting a polymer that restricts O2-transport to the catalyst (Nafion), we can suppress O2 reduction. However, CO2 transport is also impeding, leading to poor selectivity for CO formation.

社会严重依赖使用原始化石燃料作为化工和塑料制造的原料。随着脱碳压力的增加，并不是所有行业都有可能做到这一点，导致水泥、钢铁和玻璃生产商等无法完全脱碳的高二氧化碳排放者面临越来越大的经济处罚威胁。电化学二氧化碳减排提供了利用间歇性可再生能源(风能、太阳能)推动二氧化碳转化为有用产品的机会。这些产品的范围从一氧化碳(合成气的成分)到可持续航空燃料。电化学二氧化碳减排是一项成熟的技术，但由于要求快速发展，到2050年实现净零排放，对工艺规模化的挑战和机遇的研究已经加快。在这项工作中，我展示了在两种常见的电解槽中使用廉价的锰电催化剂，流动电池和零间隙电池，旨在实现比典型的间歇电化学实验更大的电流。在流动池中，与以前报道的近中性电解液中CO(JCO)的部分电流密度相比，Mn的部分电流密度增加了13.7 mA cm-2。然而，器件的稳定性很差，JCO在5小时后下降到&lt；5 mA cm-2。在碱性环境下，虽然在JCO~35 mA·cm~(-2)范围内对CO有较好的选择性，但在碱性环境下，该催化剂的活性较低。随着我们迈向脱碳过程的工业化，理解不纯气体对二氧化碳减排的重要性至关重要。通常，研究的重点是作为电解原料的超纯二氧化碳蒸气，但实际上，烟道气和捕获的二氧化碳都含有O2等杂质。因此，了解即使是很小的浓度对电解选择性和装置的影响也是非常必要的。通常，如果研究氧气的影响，设备故障机制没有得到解释，从而导致了知识鸿沟。在我使用纯二氧化碳的工作之后，我探索了低浓度的O2对锰络合物和一个简单的金催化剂的影响。我证明了5%O2的存在阻碍了二氧化碳在酸中的还原，然后我继续研究Au作为催化剂。在纯CO2中，Au的活性表现出对CO的高选择性，JCO在90 mA cm-2之间，但当引入0.25%O2时，JCO降低到80 mA cm-2。值得注意的是，O2的引入降低了设备的稳定性(运行5小时至3小时)，因为过氧化氢的形成导致(双)碳酸盐的形成增加。我表明，提供酸性环境对提高O2耐受性影响很小，但会牺牲CO选择性(45 mA cm-2到24 mA cm-2)和电池电压(2.6V到3.4V)。最后，筛选出抑制O2-还原的聚合物添加剂。我发现，通过选择一种限制O2-传输到催化剂(Nafion)的聚合物，我们可以抑制O2的还原。然而，二氧化碳的运输也受到阻碍，导致CO生成的选择性很差。