The study by means of the fast cyclic voltammetry of the cathodic (due to the proton discharge) and the anodic (due to the formed hydrogen atom discharge) background currents of bare and covered by a mercury monolayer carbon fiber electrodes in a wide domain of potentials and pH unveiled existence a large difference between electric charges passed during the negative- and the positive-going semi-cycles.
The difference, controlled by the magnitude of the applied negative potential E, abruptly increases when E < −1.4 V (SHE), stipulated by the appearance of an unpaired anodic peak around E = 0.7 V and reaches a maximum at E < −1.8 V followed by the appearance of the second anodic peak around E = −1.9 V.
The positive linear dependence between electric charges of these two anodic peaks and [H+], as well the formal potential of species generating the more negative anodic peak, points to the atomic hydrogen electrooxidation as their origin. The more negative peak relates to the atomic hydrogen diffused into the bulk electrolyte, while the more positive – to the ‘absorbed’ into the electrode open nanopores.
The significant excess (>103) of the anodic electric charge, caused by electrooxidation of the atomic hydrogen, denotes that the most part of this species is generated homogeneously due to the conversion of the field emitted electron by its strong scavenger H+.
The Fowler–Nordheim plot of the anodic peak currents of voltammetric waves associated with the atomic hydrogen electrooxidation confirms the field electron emission (FEE) hypothesis and denotes the source of the electron emission as the open nanopore with a diameter of 3–4 Å, formed between two external graphene sheets of the carbon fiber, where the strength of the electric field attains the maximal value of nearly 3 × 107 V cm−1.
The electrolytic deposition of a single metal atom, matching the electron emission site, increases the FEE by more than two orders on the electrode covered by a mercury monolayer due to the formation there of the Schottky nanojunction between the semiconducting carbon fiber and the metallic mercury layer.
In domain of potentials positive to View the MathML source the atomic hydrogen H0, a strong reductant, undergoes a fast oxidation generating another hydrogen intermediate – the molecular ion H2+ – a relative strong oxidant. These transformations occur preponderantly within the open nanopore that creates conditions for the catalytic chemical regeneration of electrochemically active species located there.