a b s t r a c tThe oscillatory electro-oxidation of methanol was studied by means of in situ infrared (IR) spectroscopy in the attenuated total reflection (ATR) configuration using a platinum film on a Si prism as working electrode. The surface-enhanced infrared absorption (SEIRA) effect considerably improves the spectroscopic resolution, allowing at following the coverage of some adsorbing species during the galvanostatic oscillations. Carbon monoxide was the main adsorbed specie observed in the induction period and within the oscillatory regime. The system was investigated at two distinct time-scales and its dynamics characterized accordingly. During the induction period the main transformation observed as the system move through the phase space towards the oscillatory region was the decrease of the coverage of adsorbed carbon, coupled to the increase of the electrode potential. Similar transition characterizes the evolution within the oscillatory region, but at a considerably slower rate. Experiments with higher time resolution revealed that the electrode potential oscillates in-phase with the frequency of the linearly adsorbed CO vibration and that the amount of adsorbed CO oscillates with small amplitude. Adsorbed formate was found to play, if any, a very small role. Results are discussed and compared with other systems.

The hollow precipitate tubes in chemical gardens conserve the nonequilibrium conditions present during their formation and are an important example of molecular processes causing complex macroscopic self-organization. We report a greatly simplified experimental model of these structures that is based on the formation of an inorganic membrane in a microfluidic device. Within this device, we induce the precipitation of Mn­(OH)2 and other metal hydroxides at the reactive interface of steadily injected NaOH and MnCl2 solutions. The resulting precipitate wall extends along the entire length of the reactor channel and can be positioned at will, and its width increases strictly in the direction of the metal solution. These thickening dynamics obey a square root law. The corresponding effective diffusion coefficient is proportional to [OH–], shows a sigmoidal dependence on [Mn2+], and also depends on the precipitating metal ion. The precipitate wall is permeable to methylene blue and strongly adsorbs methyl orange. Electron and optical microscopy reveals decaying micrometer-sized perturbations and a 40 μm thick gel-like layer on the surface exposed to the Mn2+ solution. The wall growth is also followed by in situ Raman spectroscopy. Potential applications toward materials and origins-of-life research are discussed.

To model ion transport across protocell membranes in Hadean hydrothermal vents, we consider both theoretically and experimentally the planar growth of a precipitate membrane formed at the interface between two parallel fluid streams in a 2D microfluidic reactor. The growth rate of the precipitate is found to be proportional to the square root of time, which is characteristic of diffusive transport. However, the dependence of the growth rate on the concentrations of hydroxide and metal ions is approximately linear and quadratic, respectively. We show that such a difference in ionic transport dynamics arises from the enhanced transport of metal ions across a thin gel layer present at the surface of the precipitate. The fluctuations in transverse velocity in this wavy porous gel layer allow an enhanced transport of the cation, so that the effective diffusivity is about one order of magnitude higher than that expected from molecular diffusion alone. Our theoretical predictions are in excellent agreement with our laboratory measurements of the growth of a manganese hydroxide membrane in a microfluidic channel, and this enhanced transport is thought to have been needed to account for the bioenergetics of the first single-celled organisms.

By means of in situ IR spectroscopy we investigate the effect of dissolved alkali cations on the electro-oxidation of ethylene glycol on platinum in alkaline media. The results revealed that the increase in the oxidation currents (Li(+) < Na(+) < K(+)) is reflected in the increase in the ratio between carbonate and oxalate produced.