Atomistic Insights into Electrochemical Hydrogenation of Formaldehyde for Renewable Hydrogen Storage
Abstract
The electrochemical hydrogenation of formaldehyde (FA) to methanol (MeOH) is a transformative step in renewable hydrogen storage and transport using liquid organic hydrogen carriers (LOHCs). Unlike traditional fossil-based LOHCs, the FA/MeOH pair combines competitive gravimetric hydrogen capacity (~6.3 wt%) with renewable carbon-based feedstocks, enabling direct participation in CO₂ utilization markets and providing a first-mover advantage in the green hydrogen economy. This proposal aims to theoretically investigate the fundamental electrochemical processes underlying FA reduction to MeOH using density functional theory (DFT) calculations and molecular dynamics (MD) simulations. Electrochemical hydrogenation of LOHC (e-LOHC) merges FA hydrogenation in a single-step process, offering higher efficiency (~80%) than conventional chemical routes that rely on external H₂ gas, high pressures, and elevated temperatures. To optimize this e-LOHC pathway, a detailed understanding of the catalyst surface reactions, proton/electron transfer, and double-layer effects at the electrode–electrolyte interface is essential.
1. Reference calculation
As a starting point, the uncatalyzed mechanism for the reaction of H2 with FA to generate MeOH will be investigated within the framework of DFT. The energies for the different possible pathways will be compared in the gas phase as well as in different solvent media.
2. Catalyst design
After obtaining the energetics under catalyst-free conditions, the reaction of H2 with FA will be investigated in the presence of a catalytic surface of a transition metal such as Ni or Cu. The effect of the catalyst on the activation energy for the formation of MeOH will be explored by calculating adsorption energies and hydrogenation barriers using plane-wave periodic DFT and tight-binding DFT (DFTB). In a subsequent step, the calculations will be extended to bimetallic systems such as a single Ni atom on a Cu surface or adatom sites.
3. Electrochemical environment
The influences of the electric double layer and the applied potential, as well as the surrounding solvent, will be modelled using constant-potential DFT and explicit/implicit solvent approaches, respectively. These calculations will reveal how ionic distributions and interfacial electric fields modulate the thermodynamics and the reaction kinetics.
4. Proton-coupled electron transfer (PCET)
Using plane-wave periodic DFT and DFTB, we will investigate different PCET mechanisms for the coupling between proton migration from the electrolyte and electron flow through the catalyst. These mechanisms serve to maximize Faradaic efficiency and suppress side reactions that could otherwise reduce the MeOH yield. Different possible mechanisms will be considered for PCET. In concerted PCET, the electron and the proton move in a single step with no stable intermediates. In stepwise electron/proton transfer, they move via charged intermediates. In H-atom transfer, a proton and an electron are transferred between sites in a highly correlated fashion. Classical MD, DFTB and ab initio MD (AIMD) simulations will be performed to capture the temporal evolution of solvent molecules, ion distributions, and FA molecules near the electrode. The results will support experimental validation and accelerate the development of scalable, high-efficiency e-LOHC systems.
