EAGER: New approach to rational design of efficient electrocatalysts for the oxygen reduction reaction in hydrogen fuel cells

燃料电池是通过电化学反应将燃料的化学能直接转化为电能的装置。如果成功的话，实用的燃料电池将成为转向绿色经济的关键技术。然而，燃料电池的成功应用受到与氧还原反应动力学相关的因素的阻碍。似乎需要昂贵的铂基催化剂来催化这些氧还原反应。铂当然是稀有和昂贵的，并且容易被一氧化碳等分子中毒，导致催化剂寿命缩短。尽管进行了数十年的研究，但很少发现具有有希望的氧还原催化活性的非贵金属催化剂，并且没有一种表现出足够的性能稳定性。开发作为ORR的更好催化剂的新的具有成本效益的材料的一个困难在于，存在有限的一组元素，其可以耐受PEM FC的反应环境，该反应环境是高度酸性的并且处于高操作电位。这些元素是铂、铱、金和钯，都是珍贵而稀有的。为了降低这些电极材料的成本，已经对在无铂基底上使用铂基合金或铂单层进行了研究。由于在这些合金中需要高铂百分比，成功受到限制。尽管如此，这些研究提供了有用的信息，在了解组成，几何形状，表面电子结构和ORR活动之间的关系。鉴于这些数据，人们进行了许多新材料的组合计算筛选实验。这些实验总体上缺乏合理的基础，对理解控制绩效的因素没有多大帮助。中佛罗里达大学的Sergey Stolbov教授建议使用合理的材料设计方法来指导他的计算催化剂研究。几种选定的材料和复合材料已被选择用于这一初步研究。这项工作是基于早期发表的计算结果，指向多种金属方法。代替铂，选择银作为主电极材料。虽然对反应介质的稳定性稍差，但Stolbov的计算表明，将金属支撑在合适的基底上将增加顶层对燃料电池化学条件的稳定性。此外，Stolbov的计算结果表明，这种基质材料可能有助于调节ORR反应的性能。可以添加第三金属以进一步优化该电极夹层的稳定性和行为。PI、一名女性研究助理和一名研究生将对以下夹层系统进行适当计算：银/钌/铌、银/铌、银/钨、银/钼和银/氮化铬。这个EAGER奖的结果是一组计算和数据，这些计算和数据将用于这些三明治电极的后续制造。PI和同事正在向布鲁克海文国家实验室的一个小组提供这些计算方向，该小组试图制造和评估这些电极系统，这些电极系统是由理性计算方法预测的。目前已经建立了工作关系，这些新材料将在燃料电池计划的过程中接受这些专家的评估。 PEM FC的问题是众所周知的，并由PI正确表征。一些机构已经投入了大量资金进行研究，以规避这些问题。目前还没有解决办法。Stolbov提出了一个有趣的方法，并拨了初步的实验，以适应电极费用的问题。他认为，计算结果还将反映材料对燃料电池反应介质的稳定性，并允许基于成分进行性能优化。PI意识到评估将需要其团队中不具备的专业知识，并安排了一个公认的研究小组来实现计算结果。因此，如果成功的话，结果可能真正是变革性的，并且通过计算的进一步合理设计可能为PEM FC电极问题提供更好的解决方案。这种方法可能被视为高风险，因为计算研究可能仅导致性能或材料稳定性不优于当前的贵金属电极方法。然而，如果成功的话，回报将是真正值得投资在这个渴望的建议。

Fuel cells are devices for direct conversion of the chemical energy of a fuel into electricity through electrochemical reactions. If successful, practical fuel cells would be a key enabling technology for movement to a green economy. However successful application of fuel cells has been hindered by factors relating to the kinetics of the oxygen reduction reaction. Expensive platinum-based catalysts seem to be required to catalyze these oxygen reduction reactions. Platinum is of course rare and expensive and is susceptible to poisoning by molecules such as carbon monoxide, leading to reduced catalyst lifetimes. Despite many decades of research, very few non-precious metal catalysts have been found with promising oxygen reduction catalytic activity and none have exhibited sufficient performance stability. One difficulty in developing new cost-effective materials which are better catalysts for ORR is that there are a limited set of elements that can endure the reaction environment of the PEM FC, which is highly acidic and at high operating potential. These elements are platinum, iridium, gold and palladium, all precious and rare. To reduce the costliness of these electrode materials, studies have taken place on the use of platinum-based alloys or platinum monolayers on platinum-free substrates. Success has been limited due to the necessity of high platinum percentage in these alloys. Nonetheless, these studies offer information useful in understanding the relationship between composition, geometry, surface electronic structure, and the ORR activity. Given this data, many combinatorial computational screening experiments for new materials have been made. These experiments lack a rational basis in general, and do not add much to the understanding of the factors controlling performance. Prof. Sergey Stolbov at the University of Central Florida proposes to use rational material design approaches to direct his computational catalyst studies. Several selected materials and composites have been chosen for this initial study. The work is based on earlier published computational results pointing to multiple metal approaches. Instead of platinum, silver is selected as the main electrode material. Although somewhat less stable to the reaction medium, the Stolbov's calculations have indicated that supporting the metal on a suitable substrate will increase the stability of the top layer to the fuel-cell chemical conditions. Furthermore, Stolbov has computational results which suggest that this substrate material may help tune the performance in the ORR reaction. A third metal may be added to further optimize the stability and behavior of this electrode sandwich. The PI, a female research associate, and a graduate student will conduct appropriate computation for the following sandwich systems: silver/ruthenium/niobium, silver/niobium, silver/tungsten, silver/molybdenum, and silver/chromium nitride. What will result from this EAGER award is a set of computations and data which will be used in the subsequent fabrication of these sandwich electrodes. BROADER IMPACTS The PI and associates are providing these computational directions to a group at Brookhaven National Laboratory, which is attempting to fabricate and evaluate these electrode systems predicted by the rational computational approach. A working relationship is already present, and these new materials will be subject to evaluation by these experts in the course of their program on fuel cells. The problems with PEM FCs are well-known and correctly characterized by the PI. Several agencies have invested many dollars in research to circumvent these problems. No solution is yet in hand. Stolbov proposes an interesting approach and has dialed the initial experimentation to accommodate the question of electrode expense. He believes the computational results will also read on the stability of the materials to the fuel-cell reaction medium, and will also allow for performance optimization based on composition. The PI realizes the evaluation will require expertise that is not available in his group, and has arranged for a recognized research group to actualize the results of the computations. Thus, if successful, the results may truly be transformative, and further rational design through computation may offer even better solutions to the PEM FC electrode problem. This approach may be viewed as high-risk in that the computational studies may lead only to performance or material stability that is no better than the current precious metal electrode approach. However if successful, the rewards will truly be worth the investment in this EAGER proposal.