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Herein, we advance our fundamental understanding of hydrogen electrochemistry as crucial energy technology by challenging the century-long paradigm that Volmer, Heyrovsky, and Tafel reactions are elementary. We identify and resolve the theoretical controversy of this phenomenological model to argue that each reaction must be stepwise not concerted elementarily. The stepwise model provides unprecedented insights as exemplified by resolving current debates on the Tafel analysis and volcano plot based on the controversial concerted model. The stepwise mechanism has not been distinguished from the concerted mechanism experimentally owing to the Laviron–Amatore paradox, which will be overcome by developing transient nanoelectrochemical methods.

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The electrochemical behavior of heme-phorphyrin iron (III) centered hematin (Htin) was investigated at a Htin modified glassy carbon electrode with cyclic, differential pulse, square wave voltammetry in different pH values. For all pH values, the electrochemical process attributed to the reduction of hematin follows an EE mechanism, in which the ligand suffers mediated electrochemical reduction by the iron metallic center. At the backward scan, the same mechanism is observed for the oxidation of hematin in pH > 5.5. However, the electrochemical oxidation at backward scan in pH < 5.5 occurs firstly and directly at the ligand with the formation of IS (intermediate specie) that is further oxidized at the metallic center and forms Fe(Htin) 3+ . In acid and neutral media, the oxidation of hematin at the positive potential range is an irreversible and pH-dependent process that follows an ECE mechanism. In the first step, the electrochemical oxidation of hematin involves the transfer of one electron from the pyrrolic nitrogen heteroatom with the formation of a cationic radical that loses its iron (III) center in a subsequent chemical step. The resulting cationic radical suffers further oxidation to produce a structure similar to the protoporphyrin IX.

Sulfasalazine (SSZ) is a pharmaceutical compound used for the treatment of rheumatoid arthritis. The electrochemical oxidation of SSZ at a glassy carbon electrode was studied by cyclic, differential pulse and square wave voltammetry in a wide pH range. For electrolytes with pH<11.0, the oxidation is an irreversible, diffusion‐control, pH‐dependent process that involves the transfer of one electron and one proton from the hydroxyl group of the salicylic moiety. For pH>11.0 the oxidation is pH‐independent, and a pKa≈11 was determined. The formation of a quinone‐like oxidation product that undergoes two electrons and two protons reversible redox reaction was observed. Also, UV‐vis spectra of SSZ were recorded as a function of supporting electrolytes pH. An electrochemical oxidation mechanism was proposed.

A PROPOSITION FOR TEACHING LABORATORY OF QUALITATIVE ANALYTICAL CHEMISTRY. Teaching laboratory of qualitative analytical chemistry is still a controversial issue in chemistry courses. However, important researchers and educators in chemistry recognized and highlighted the importance that the contents of this discipline represent in the formation of chemists, once it can provide handling and understanding of microscopic phenomena based on the observation of their macroscopic effects, once such reactions and phenomena are the basis of important instrumental methods of analysis. Thus, a proposal based on a bottom-up approach has been developed, starting with the observation of different reactions of cations in laboratory, followed by a search for the reaction responsible for each resulting phenomenon observed during the experimental step. Then these reactions are related with the separation procedures of each group of cations. Eventually the separation of these groups can also be performed depending on the time available. The proposal has been applied in teaching laboratory of qualitative analytical chemistry at Instituto de Química de São Carlos/USP since 2015, where the discipline is offered duirng 4 hours/week, and a positive feedback regarding the evolution of the methodology and its acceptance by students. Good results were also obtained concerning the appropriation of the contents by the students, using the proposal.