(362k) Grand Canonical Potential Kinetics (GCP-K) for Electrochemical Reactions from Quantum Mechanics
AIChE Annual Meeting
2023
2023 AIChE Annual Meeting
Engineering Sciences and Fundamentals
Faculty Candidates in CoMSEF/Area 1a, Session 1
Monday, November 6, 2023 - 9:40am to 9:50am
The GCP-K arises from the minimization of the fixed charge based free energy, F (n), using a Legendre transformation to grand canonical free energy, G (n; U), allowing the thermodynamic free energy for heterogeneous electrochemical reactions to depend on the applied potential (U) (Fig. 1)
G(n;U) = F (n) - ne(USHE-U)
Where G is the grand canonical free energy, which depends on applied voltage U vs SHE, n is the number of electrons, e is the unit electronvolt in energy, F is DFT energy as a function of n, and USHE = µe,SHE/e is the chemical potential of electron at the standard hydrogen electrode (SHE) condition. The signs are analogous to experimental value i.e., U= - 0.1 V corresponds to -0.1 V vs SHE. The GCP-K methods allows change of the geometry at the transition states and the charge transfer from electrode to adsorbed species continuously as a function of applied potential alone the reaction pathways.
In the first application of our GCP-K method, we predict the HER activity (current as a function of U) as a function of Te vacancy concentration for the basal plane of both the 2H and 1Tâ² phases of MoTe2 with experimental validation. This method allows us to describe the transition state energy barrier change with applied potential as a result of structural change. The energy barrier further converted into the turnover frequency (TOF) and current density as a function of potential using a micro-kinetics model. To validate the accuracy of the GCP-K predictions, our experimental collaborator synthesized both phases of MoTe2 monolayer materials and created controlled Te vacancy by applying Ar plasma. Using GCP-K method, we predict an overpotential of 535 and 565 mV to achieve current density of 10 mA cm-2 for 1Tâ²-MoTe2 and 2H-MoTe2 containing 1.14 x 1014 cm-2 and 3.45 x 1013 cm-2 Te vacancies respectively. Which shows good agreement with experimental overpotentials of 561 and 634 mV for 1Tâ²-MoTe2 and 2H-MoTe2 containing similar vacancy concentrations ( 1.28 x 1014 cm-2 and 3.54 x 1013 cm-2).
In the last part of presentation, I will be talking about GCP-K application for CO2RR on Ni-single atom catalysts (Ni-SACs). We applied the GCP-K method to determine the reaction mechanism and kinetics for CO2RR on different nitrogen coordination such as Ni-N2C2, Ni-N3C1, and Ni-N4. We find each site has unique reaction kinetics with Ni-N2C2 initiates current at early potential and produces Uonset =-0.84 V, with a Tafel slope of 52 mV decâ1, a faradic efficiency (FE) of 98%, and TOF = 3903 hâ1 per Ni site. On the other hand, Ni-N3C1 shows an onset potential of -0.92 V, with higher Tafel slope of 62 mV decâ1, a lower FE = 78% and TOF = 2940 hâ1 per Ni site. Finally, Ni-N4 dominant for U < â1.05 V producing 10 mA cmâ2 at -1.03 V applied potential with a Tafel slope of 55 mV decâ1, a FE = 99% faradic efficiency, and TOF = 3944 hâ1 per Ni site. These predicted results show reasonable agreement with experience experimental studies.
In order to help guide identification of the sites in experimental synthesized Ni-SACs, we predict the CO vibrational frequencies for various sites. The CO stretch for CO bound to Ni is 1985 cmâ1 at -1.0 V on Ni-N2C2 site and 1942 cmâ1 at -1.25 V on Ni-N4 site. As compared with literature, Ni-N2C2 site shows best fit with experiment, but we expect that synthesized Ni-SACs have different proportions of all three Ni sites and the resulted overall activity originates from each of them.
References
1. Yufeng Huang et al., Reaction mechanism for the hydrogen evolution reaction on the basal plane sulfur vacancy site of MoS2 using grand canonical potential kinetics, J. Am. Chem. Soc. 2018, 140, 48, 16773â16782.
2. Md Delowar Hossain et al., Reaction Mechanism and Kinetics for CO2 Reduction on Nickel Single Atom Catalysts from Quantum Mechanics; Comm., 2020, 11 (1), 1-14.
3. Jie Song et al., Reaction Mechanism and Strategy for Optimizing the Hydrogen Evolution Reaction on Single-Layer 1Tâ² WSe2 and WTe2 Based on Grand Canonical Potential Kinetics; ACS Appl. Mater. Interfaces, 2021, 13, 46, 55611â55620.
4. Md Delowar Hossain et al., The Kinetics and Potential Dependence of the Hydrogen Evolution Reaction Optimized for the Basal Plane Te Vacancy Site of MoTe2, 2023, Chem Catal., 100489.