Electrocatalyst Design for Direct Borohydride Oxidation Guided by First Principles

Janik, Michael J.; Rostamikia, Gholamreza; Patel, Romesh J.; Merino-Jimenez, Irene; Hickner, Michael

Abstract

© 2017 American Chemical Society. Density functional theory (DFT) calculations are used to propose a Au-Cu binary metal catalyst for the electrochemical borohydride oxidation reaction (BOR), which is evaluated experimentally and observed to show enhanced oxidation activity relative to a pure Au electrode. Our previous work has applied DFT methods to determine the BOR mechanism and elucidate the key reaction steps that dictate catalyst activity and selectivity to complete oxidation. A balanced initial adsorption strength of the borohydride anion is essential for an active and selective catalyst. Adsorption must be strong enough to provide a reasonable coverage of surface species and promote B-H bond dissociation but not so strong as to promote easy dissociation and provide a high coverage of surface H atoms that result in H 2 evolution. Borohydride adsorption energetics were evaluated for a series of close-packed pure metal surfaces. Copper catalysts appear encouraging but are not electrochemically stable under reaction conditions. Gold-copper alloys are predicted to show increased activity compared to a pure gold electrode while maintaining the selectivity to direct oxidation and increasing the stability compared to pure Cu. DFT results suggest an approximately 0.2 V decrease in the overpotential for borohydride oxidation on a Au 2 Cu(111) electrode compared to that on a Au(111) electrode. This DFT-predicted reduction in overpotential is realized experimentally. Electrodeposition was used to prepare AuCu electrodes, and their borohydride oxidation electrokinetics were examined by linear sweep voltammetry. An 88.5% gold and 11.5% copper sample demonstrated an overpotential reduction of 0.17 V compared to a pure Au electrode. The binding energy and adsorption free energy of BH 4- over other surface alloys are also examined to further identify promising BOR electrodes. (Chemical Equation Presented).

• Journal Article Type: Article
• Acceptance Date: Jan 11, 2017
• Publication Date: Feb 9, 2017
• Deposit Date: May 12, 2017
• Publicly Available Date: Jan 17, 2018
• Journal: Journal of Physical Chemistry C
• Print ISSN: 1932-7447
• Electronic ISSN: 1932-7455
• Publisher: American Chemical Society
• Peer Reviewed: Peer Reviewed
• Volume: 121
• Issue: 5
• Pages: 2872-2881
• DOI: https://doi.org/10.1021/acs.jpcc.6b12159
• Keywords: electrocatalyst design, direct borohydride oxidation, first principles
• Public URL: https://uwe-repository.worktribe.com/output/899942
• Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.6b12159
• Additional Information: Corporate Creators : Department of Chemical Engineering, Pennsylvania State University, University Park, PA 16802, Department of Materials Science and Engineering, Pennsylvania State University, University Park, PA 16802, Bristol Robotics Laboratory, Universities of Bristol and of the West of England, Bristol Business Park, Coldharbour Lane, BS16 1QY, UK
• Contract Date: May 12, 2017