Resonance-Promoted Formic Acid Oxidation via Dynamic Electrocatalytic Modulation

Abstract

It is a truth universally acknowledged that faster catalysts enable the more efficient transformation of molecules to useful products and enhance the sustainable utilization of natural resources. However, the limit of <i>static</i> catalyst performance defined by the Sabatier principle has motivated a new approach to <i>dynamic</i> catalyst design, whereby catalysts oscillate with time between varying energetic states at sufficiently high resonant frequencies to overcome the Sabatier ‘volcano peak’. In this work, the concept of dynamic catalytic resonance was experimentally demonstrated via the electro-catalytic oxidation of formic acid in water on a Pt working electrode within a semi-continuous multi-phase flow reactor. Steady-state electro-oxidation of formic acid at 0.6 V (NHE) exhibited a maximum turnover frequency (TOF) of CO<sub>2</sub> formation of ~1.0 s<sup>-1</sup> at room temperature. However, oscillation of the electrodynamic potential between 0.8 V and open circuit via a square waveform at varying frequency (10<sup>-3</sup> < <i>f</i> < 10<sup>3</sup> Hz) increased the optimal TOF to ~5 s<sup>-1</sup> at 0.5 Hz. An even higher TOF of ~20 s<sup>-1</sup> was observed at a resonant frequency of 100 Hz for a square waveform oscillating between zero and 0.8 V. The rate increase in formic acid electro-oxidation via catalytic resonance of more than an order of magnitude (20x) above potentiostatic conditions was interpreted to occur by non-faradaic formic acid dehydration to surface-bound carbon monoxide at low potentials, followed by surface oxidation and desorption to carbon dioxide at high potentials.

Increasing stability, efficiency, and fundamental understanding of lithium-mediated electrochemical nitrogen reduction

“…This motivates repeated deposition-resting cycles to improve the efficiency of the Li-mediated process. Such a potential cycling approach has been used in the past to maintain stability of electrochemical systems [29]- [31], prevent electrocatalyst poisoning [32], or selectively promote specific reaction mechanisms [33]. Here, this concept is used to store and subsequently release high-energy electrons in order to continuously produce ammonia throughout the cyclic process.…”

Electric-Field Assisted Modulation of Surface Thermochemistry

“…In contrast, CO and halides (F 2 and Cl 2 ) are known to poison the catalyst surface (adsorption energy > -1.8 eV). [67][68] For reactions efficiently catalyzed on Pt (for example, HCOOH and NH 3 oxidation), 20 the substrates are chemisorbed (adsorption energy of ~ -0.6 eV for HCOOH, and ~ -1.0 eV for NH 3, see Table 1).…”

“…19 As such, the time-averaged catalytic activity can be enhanced above the Sabatier maximum as the catalytic system switches between rate-limiting steps, as demonstrated by a recent experimental work on the electro-oxidation of formic acid to carbon dioxide and hydrogen. 20 Recently, this potentiodynamic operation was utilized for selective enhancement of electrosynthesis of adiponitrile (main precursor to Nylon-66) by ~325% from acrylonitrile compared to potentiostatic operation, in favor of competing production of propionitrile 21 The adsorption energies of adsorbates need to uniquely vary for a dynamic system to provide enhanced reactivity under the same dynamic stimuli. [17][18] Materials design approaches that involve the optimization of catalyst composition have not yet been shown experimentally to assist with overcoming the Sabatier maximum, as the adsorption energies of key surface intermediates are typically bound to the same periodic linear scaling relationships.…”

Multiscale Models in Heterogeneous Catalysis: Incorporating Dynamics into Reaction Kinetics

“…Indeed, Thomas and Thomas 12 provided extensive details on dynamic modelling during catalyst deactivation. Ertl 30 , Kobayashi [31][32][33][34] , Dauenhauer 35,36 , Carroll 37,38 and Boudart 39,40 studied reaction dynamics. Warshel [41][42][43][44][45] investigated the dynamic phenomena during enzyme catalysis and observed that the duration of the kinetics of catalytic transformation is much smaller than conformational dynamics.…”