The inherent complexity of dynamical interactions between atoms and molecules charged and 
uncharged at a liquid – solid interface offers fertile grounds for obtaining a fundamental 
understanding of microscopic factors that control several phenomena relevant to sustainability. A 
case in point is the electrochemical environment in which molecular dynamics, proton coupled 
electron transfer, electric fields, electrostatics, and the making and breaking of bonds are in full 
play. In this talk, I will focus on atomistic processes and reaction mechanisms that determine the 
efficacy of the electrochemical environment for CO2 reduction reaction (CO2RR) and hydrogen 
evolution reaction (HER).  I will summarize our computational and experimental findings that 
non-metal ammonium-based cations can have an even more profound effect on CO2 adsorption 
characteristics and both CO2RR and HER activity than the popular alkali metal cations. Ab initio 
calculations based on grand canonical density functional theory (GC-DFT) show that both NH4+ 
and CH3NH3+ bind CO2 to a metal (Au, Pt) or semimetal (Bi) electrode more strongly than Na+ or 
K+ and track the difference to the directional geometry of the local electrostatic field between the 
cations and adsorbed CO2, benefiting from the charge distribution and hydration shell of the 
cations. Furthermore, on immobilized cobalt phthalocyanine (CoPc) supported on carbon 
nanotubes (CoPc/CNTs) we identify the rate-limiting step of CO2RR to CO to be the protonation 
of adsorbed CO2, whereas CO2 adsorption is the one on metal electrodes. Here ammonium-
based cations achieve a 10-fold improvement in the CO2RR activity compared to Na+, while 
maintaining a Faradaic efficiency of 95% for CO production. Operando X-ray absorption 
spectroscopy and computational analyses reveal a dual role of the ammonium cations as a strong 
promoter of CO2 adsorption on the Co active site and a unique proton donor for *CO2 protonation 
to *COOH via a proton shuttling mechanism. These studies demonstrate the power of modern 
techniques not only in the rational selection of cations for CO2RR and HER but also in the 
designing of the solid-liquid interface for a variety of applications.