Electrosynthesis via Plasma Electrochemistry: Generalist Dynamical Model To Explain Hydrogen Production Induced by a Discharge over Water

Abstract

Electrosynthesis via electrochemical plasma, a discharge over the surface of liquid water (or plasma cathode), may offer an unprecedented route of synthesis for chemicals and (wind) solar fuels. Describing the physical chemical events underneath plasma/liquid interface (PLI) on a theoretical basis is crucial for enabling a rational designing of chemical synthesis. To address this problem, this work proposes a generalist dynamical model for the nanoreactor, a fraction of nanoliters localized beneath the PLI that features substantially high concentration of hydrated electrons (e aq –), and it screens chemical reaction networks (CRN) related to the synthesis of hydrogen, a model electrosynthesis process. The computational results elucidate two major routes for hydrogen production: (a) in very alkaline media, the water reduction via self-recombination of e aq – [2e aq – + 2H2O → H2 + 2OH–] consumes the majority of e aq –, whereas (b) in very acid media, e aq – is majorly scavenger by the ion H aq +, generating an abnormally high concentration of the radical H•, a precursor for gaseous hydrogen. Additionally, two scenarios are disadvantageous for synthesizing H2. Side reactions with aqueous oxygen and aqueous radical •OH leads to substantial production of O2 – and OH–, respectively. Without loss of generality, the dynamical model proposed in this work is a powerful theoretical frame for understanding and predicting a variety of plasma-induced CRNs, assisting to advance the emerging field of plasma electrochemistry.

The Electrified Plasma/Liquid Interface as a Platform for Highly Efficient CO2 Electroreduction to Oxalate

“…Gaseous hydrogen is a volatile product synthesized mainly via the recombination of two solvated electrons (reaction ). The other two routes for hydrogen synthesis, described in ref , demonstrated negligible contributions over the continuous long-lasting discharge tested in this work. In essence, the concentration of the hydronium ion depletes faster than that of dissolved CO 2 (CO 2 (aq)) when a complete CNR considers the formation of radical H. Section E in the Supporting Information explains the full details of this claim.…”

“…Second, the physical correctness of the value attributed to the reactor volume was evaluated and its limit was tested. This work used a value of 2.36 × 10 −9 L according to Table 1, merely reproducing the value employed in our previous theoretical work; 30 however, our very early analysis 27 argued for a volume of 13.3 × 10 −12 L with some fractions of nanoliters. In order to understand this difference, we must ponder the fact that both the PLI area and the solvated electron penetration depth define the reactor geometry.…”

“…The parameter q e quantifies the number of ballistic electrons, those electrons that are accelerated by the large electric field in the plasma phase, that transform into hydrated electrons after collision with the surface of the liquid. The value of q e was estimated by the electrical current (I) divided by the Faraday constant 30 q I 96485 e = (8) Furthermore, the source term q CO 2 considers the liquid uptake of CO 2 or the CO 2 dissolution via the liquid or gas phase. However, we found that q CO 2 ≪ k 2 , leading to an attribution of q CO 2 = 0 as a result of k q CO (aq) e (aq)…”

“…The generalist model described in ref for plasma-induced chemistry was employed in order to implement the algorithm related to the CNR tree displayed in Figure , resulting in a set of ordinary differential equations related to both the reactants and the intermediate species, the carboxyl radical anion CO 2 −• (aq) …”

“…To this end, data sets from the radiolysis field , are inspected in order to sort out the most prominent steps by considering the hydrated electron, aqueous carbon dioxide, or water as the primary reactant. The theoretical framework described earlier is employed in order to study the chemical dynamics of the postulated CO2RR mechanism. After validating the proposed mechanism through fair agreement with the features observed in real life experiments, this work suggests an insightful strategy allowing for 97% selectivity to oxalate.…”