Prefreezing is the prewetting of the crystalline phase at the interface of a melt to a solid substrate via a first-order phase transition. We present a phenomenological theory of prefreezing and analyze thermodynamic properties of the prefrozen crystalline layer. The theory enables a clear thermodynamic explanation of the abrupt formation of a mesoscopically thick crystalline layer during cooling and defines the corresponding transition temperature as a function of the interfacial free energies. It is shown that the interfacial energy difference γ_sm−(γ_sc+γ_cm) acts as a driving force for prefreezing. The analytical results are congruent with recent experimental outcomes for poly(ε-caprolactone) crystallized on graphite via prefreezing. The calculated interfacial free energies take reasonable values being close to the experimental estimates.

The Oxygen and nitrogen plasma treatment were applied to produce graphene with abundant edges, oxygen functional groups, and nitrogen doping. The plasma-etched graphene was then used as a metal-free electrocatalyst in a solid acid fuel cell. Scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy were used to characterize the graphene layers. Alternating-current impedance spectroscopy of a hybrid electrode containing the plasma-etched graphene and cesium dihydrogen phosphate as proton-conducting solid acid illustrated its remarkable catalytic activity under cathodic conditions. Thus, both O₂ and N₂ plasma treatment activated the material. While O₂ plasma was a more effective activator than N₂ plasma, it also resulted in higher degradation rates. A combination of density functional theory calculations and experimental results indicated that zigzag carbon was the most active site for the oxygen reduction reaction on both O₂ and N₂ plasma-etched graphene. Furthermore, the armchair carbons adjacent to the surface oxygen groups and doped heteroatoms were also important active sites for O₂ and N₂ plasma-etched graphene, respectively. The results of this study will guide future endeavors in the development of non-precious metal catalysts for use as fuel cell cathodes.

Titanium, either in the form of a Ti foil or in form of a Ti mesh, was used as a novel substrate to grow nitrogen‐doped carbon nanotubes (NCNTs) through chemical vapor deposition at moderate temperatures over electrodeposited iron particles. The thus‐prepared high‐surface‐area electrodes were characterized by scanning electron microscopy (SEM), Raman spectroscopy, and X‐ray photoelectron spectroscopy (XPS). The electrochemical performance towards the V(IV)/V(V) redox couple was investigated by cyclic voltammetry. The parameters for iron particle electrodeposition were adjusted towards high and uniform substrate coverage. Nanotube growth from acetonitrile at moderate temperatures (600 °C) led to N‐containing CNTs with a high amount of graphitic nitrogen. NCNTs grown over Ti substrates provide promising performances towards the V(IV)/V(V) as well as the V(III)/V(IV) redox pair. In general, the results of this study show that Ti might be a suitable electrocatalyst substrate for various applications in electrochemical energy conversion.