The kinetics of electrochemical reactions are commonly described by the Butler-Volmer model. It has been pointed out that this model is after all a phenomenological model, meaning that it has been built "top down" from observation rather than from well-established physical theory. Therefore, much effort has been taken to build a framework of electrochemical kinetics from first principles both by classical and quantum mechanics. Of note are the Marcus model, the MHC theory and other specific theories such as the PCET theory. The latter reflects that the most researched electrokinetic reactions involve the transfer of a proton where it is clear from recent research that the classical Butler-Volmer model is incapable of describing such reactions .