Electric-Field-Assisted Formic Acid Decomposition at Ambient Conditions for Carbon Neutral Hydrogen Production

氢燃料电池提供了当今最清洁、最节能的能源。氢(H2)的清洁产生及其分布和储存对传统的化石燃料起始材料提出了挑战。相比之下，该项目在以水(H2O)和二氧化碳(CO2)为起始材料的再生循环中使用甲酸(HCOOH)作为氢载体。目前，贵金属催化剂的高昂成本--分解甲酸和产生氢气--限制了该技术的商业实施。该项目研究了一种新的概念，通过这种概念，在电场辅助燃料重整装置的帮助下，可以使铜(Cu)或镍(Ni)等活性较低、成本较低、富含地球的催化材料具有与贵金属一样的性能，该装置将产生氢气为燃料电池提供动力。研究人员计划开展几项教育和推广活动，以展示这项技术，同时还教育各级学生如何通过电化学和催化来促进向可持续能源未来的过渡。基于二氧化碳的可再生燃料电池技术的潜在应用为基于非化石能源的未来能源系统提供了有趣的前景。由于CO2选择性电化学还原为HCOOH的动力学是有利的，利用HCOOH分解制氢的按需制氢的再生燃料电池系统具有很高的实用前景。然而，最有效的HCOOH分解催化剂需要大量昂贵的贵金属，如铂(Pt)和钯(Pd)。富含稀土的纯铜在高温下表现出对HCOOH分解的高活性和选择性，但在常温下没有活性。通过在表面施加最佳强度和取向的电场，可以绕过这一限制。在环境条件下，外加电场将显著提高HCOOH在铜和镍金属上分解生成H2/CO2的速率，同时防止其导致H2O/CO生成的不良副反应。该项目将探讨外加电场如何影响HCOOH分解动力学和金属表面催化性能的基本方面，方法是利用场离子/电子显微镜结合原子探针质谱仪进行详细的动力学研究，并使用原位FTIR研究表面中间体和外加电场之间相互作用的性质(取向和相对吸附能)。基于这一基本的电场-活性-选择性关系，我们将制备并评价一个实验室规模的HCOOH重整体系。HCOOH分解是研究外加电场对金属催化性能影响的理想模型反应，因为它具有显著的永久偶极矩和高极化率，这使得其化学对周围电场的变化非常敏感。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Hydrogen-powered fuel cells offer the cleanest and most energy-efficient source of power available today. Clean generation of hydrogen (H2) and its distribution and storage present challenges with conventional fossil fuel starting materials. In contrast, this project utilizes formic acid (HCOOH) as a hydrogen carrier in a regenerative cycle based on water (H2O) and carbon dioxide (CO2) as the starting materials. Currently, the high cost of precious metal catalysts - needed to decompose the formic acid and generate the hydrogen - limits the commercial implementation of the technology. The project investigates a novel concept by which less active, low-cost, earth-abundant catalytic materials such as copper (Cu) or nickel (Ni) can be made to perform like the precious metals with the aid of an electric field-assisted fuel reforming unit that will generate the hydrogen to power the fuel cell. The investigators plan several educational and outreach activities to demonstrate the technology while also educating students at all levels on the ways in which electrochemistry and catalysis can facilitate the transition to a sustainable energy future. The potential use of CO2-based regenerative fuel cell technology holds interesting prospects for future energy systems based on non-fossil energy sources. Because the kinetics of the selective electrochemical reduction of CO2 to HCOOH are favorable, a regenerative fuel cell system utilizing on-demand H2 production from HCOOH decomposition is highly promising for practical purposes. However, the most efficient catalysts for HCOOH decomposition require a large amount of expensive noble metals such as platinum (Pt) and palladium (Pd). Earth-abundant pure Cu metal has shown both high activity and selectivity toward HCOOH decomposition at elevated temperatures, but no activity at ambient temperatures. This limitation can be circumvented by applying an electric field of optimum strength and orientation to the surface. The applied field will significantly increase the rate of HCOOH decomposition toward H2/CO2 production over Cu and Ni metals at ambient conditions, while preventing its undesired side reaction that leads to H2O/CO production. The project will address fundamental aspects of how this applied electric field influences both the HCOOH decomposition kinetics and catalytic properties of the metal surface through detailed kinetic studies utilizing field ion/electron microscopy in combination with atom-probe mass spectrometry, and by investigating the nature of the interactions (orientation and relative adsorption energy) between surface intermediates and an applied field using in-situ FTIR. Based on this fundamental electric field-activity-selectivity relationship, a lab-scale HCOOH reforming system will be fabricated and evaluated. HCOOH decomposition is an ideal model reaction to investigate the effect of an applied electric field on the catalytic properties of metals because of its significant permanent dipole moment and high polarizability, which makes its chemistry very sensitive to changes in surrounding electric fields.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.