The electronic structure calculation spontaneously separates an electron from the extra hydrogen in the water layer to form a double layer capacitor.

Absolute standard hydrogen electrode potential (ASHEP) from the calculated work function

Standard hydrogen electrode and potential of zero charge in density functional calculations

Adjust # of hydrogen atoms

Modeling the electrified solid-liquid interface

Capacitor model

Electrochemical Barriers Made Simple
Potential Dependence of Electrochemical Barriers from ab Initio Calculations

The surface charging method

Impacts of electrode potentials and solvents on the electroreduction of CO2: a comparison of theoretical approaches

Constant electrode potential (CEP) model

a self-consistent procedure in which the number of electrons in the unit cell is altered and allowed to be fractional so that the Fermi level, EF, matches the electrode potential. In other words, iterative DFT calculations with varying number of electrons are carried out in electrolyte media.
Identification of Possible Pathways for C–C Bond Formation during Electrochemical Reduction of CO2
Mechanism of CO2 Reduction at Copper Surfaces: Pathways to C2 Products


reference
Barriers of Electrochemical CO2 Reduction on Transition Metals