Structural Electrochemistry from Freestanding Polypyrrole Films: Full Hydrogen Inhibition from Aqueous Solutions

Abstract

Free-standing polypyrrole fi lms, being the metal-polymer contact located several millimeters outside the electrolyte, give stationary closed coulovoltammetric (charge/potential) loop responses to consecutive potential sweeps from -2.50 V to 0.65 V in aqueous solutions. The continuous and closed charge evolution corroborates the presence of reversible fi lm reactions (electroactivity), together high electronic and ionic conductivities in the full potential range. The closed charge loop demonstrates that the irreversible hydrogen evolution is fully inhibited from aqueous solutions of different salts up to -2.5 V vs Ag/AgCl. The morphology of the closed charge loops shows abrupt slope changes corresponding to the four basic components of the structural electrochemistry for a 3D electroactive gel: reduction-shrinking, reduction-compaction, oxidation-relaxation, and oxidation-swelling. Freestanding fi lms of conducting polymers behave as 3D gel electrodes (reactors) at the chain level, where reversible electrochemical reactions drive structural conformational and macroscopic (volume variation) changes. Very slow hydrogen evolution is revealed by coulovoltammetric responses at more cathodic potentials than -1.1 V from strong acid solutions, or in neutral salts self-supported blend fi lms of polypyrrole with large organic acids. Conducting polymers overcome graphite, mercury, lead, diamond, or carbon electrodes as hydrogen inhibitors, and can compete with them for some electro-analytical and electrochemical applications in aqueous solutions.

Bending Monolayer Artificial Muscle

“…Pictures from the transversal section of the material also show (Figure ) a more packed structure of the film at the polymer‐metal interface and a most open structure at the polymer‐solution interface of the polymer during electropolymerization. The irreversible charge detected during the coulo‐dynamic characterization is related to the hydrogen production from the HDBS component, being also the origin of the progressive slow degradation process as observed in Figure a. After 50 cycles and after correction of the creeping shift the amplitude of the displacement decreases by 7 %.…”

“…Positive charge increments are spent to oxidize the film and negative charge increments, for the film reduction. The open part, Figure b, reveals the charge consumed by irreversible reactions originated by the HDBS component . This irreversible charge results in a slow degradation of the film electroactivity, as deduced from decreasing reversible charges.…”

“…After 50 cycles and after correction of the creeping shift the amplitude of the displacement decreases by 7 %. Self‐supported films of polypyrrole generated in presence of small ions and exchanging anions during oxidation/reduction do not produce such irreversible charge and degradation, even after cycling until more cathodic potential limits …”

Self-Supported Polypyrrole/Polyvinylsulfate Films: Electrochemical Synthesis, Characterization, and Sensing Properties of Their Redox Reactions

“…In the case of polymers exchanging cations during electrochemical reactions, the reduction at increasing cathodic overpotentials leads to the formation of more energetically stable structures such as lamellas, micelles, and vesicles . Under constant temperature and at a constant electrolyte concentration, the only energetic source during the reaction is the applied potential.…”

“…The coulovoltammetric open part on the left side observed at the lower scan rate represents the irreversible charge. This is the charge consumed by irreversible reactions (hydrogen evolution) occurring in parallel to film reduction at high cathodic potentials. The irreversible charge increases for decreasing scan rates (Figure a) in the potential range studied.…”