Probing the Dissolved Gas Concentration on the Electrode through Laser-Assisted Bubbles

We demonstrate that the irradiation of a single laser pulse onto the electrode assists the formation of bubbles, and this phenomenon can be conveniently used to probe the dissolved gas concentration on the electrode. The obtained concentrations agree well with the values inferred through linear extrapolation of gas concentration in proximity to the electrode to the electrode surface

Probing the Dissolved Gas Concentration on the Electrode through Laser-Assisted Bubbles

We demonstrate that the irradiation of a single laser pulse onto the electrode assists the formation of bubbles, and this phenomenon can be conveniently used to probe the dissolved gas concentration on the electrode. The obtained concentrations agree well with the values inferred through linear extrapolation of gas concentration in proximity to the electrode to the electrode surface

Probing the Dissolved Gas Concentration on the Electrode through Laser-Assisted Bubbles

We demonstrate that the irradiation of a single laser pulse onto the electrode assists the formation of bubbles, and this phenomenon can be conveniently used to probe the dissolved gas concentration on the electrode. The obtained concentrations agree well with the values inferred through linear extrapolation of gas concentration in proximity to the electrode to the electrode surface

Platinum-Based Electrocatalysts for the Oxygen-Reduction Reaction: Determining the Role of Pure Electronic Charge Transfer in Electrocatalysis

In the oxygen-reduction reaction (ORR), electronic charge transfer (ECT) derived from alloy components and support materials generates noticeable impact on the electrocatalytic activity of Pt. However, generally, ECT will not individually occur; thus, its role remains controversial. Here, using different amount of Au to decorate Pt nanoparticles, ECT from Au to Pt is isolated to correlate with the ORR activity of Pt. The linear correlation, where pure ECT (assessed by Pt 5d orbital vacancy) depresses the adsorption of oxygenated species to enhance the ORR activity, predicts that the maximum activity enhancement should be smaller than 200%. These findings highlight that the ECT effect in the ORR is weaker than the previously reported size, facet, or strain effects, which establishes a basis for understanding exceptional ORR electrocatalysis and developing efficient Pt-based electrocatalysts

Correlation between the Forming Sites of Hydrogen Bubbles and Micro/Nanostructures on the Electrode Surface

We investigate the correlation between the forming sites of hydrogen bubbles and micro/nanostructures on the electrode surface. For this purpose, we optically monitor the formation of hydrogen bubbles over a wide area on a vertical Ni disk cathode during water electrolysis from the front of the cathode surface to identify the bubble forming sites, and label them on the surface profile of the same area with ∼μm accuracy. It turns out that these sites have very shallow microholes with a few tens of μm width and a few hundred nm depth. However, neither the width nor the depth of such holes has a clear correlation with the growth rates or formation periods of bubbles. Instead, irrespective of the local surface morphologies of the bubble forming sites, the growth rates and formation periods of the bubbles exhibit a clear correlation, and these findings strongly imply that the other factor, probably the local convection, plays a more important role to determine the fates of bubbles

Probing the Dissolved Gas Concentration on the Electrode through Laser-Assisted Bubbles

We demonstrate that the irradiation of a single laser pulse onto the electrode assists the formation of bubbles, and this phenomenon can be conveniently used to probe the dissolved gas concentration on the electrode. The obtained concentrations agree well with the values inferred through linear extrapolation of gas concentration in proximity to the electrode to the electrode surface

Hemoglobin Pyropolymer Used as a Precursor of a Noble-Metal-Free Fuel Cell Cathode Catalyst

The partial pyrolysis of hemoglobin yielded the hemoglobin pyropolymer, which is an intermediate substance between a polymer and carbonaceous material. The pyropolymer was formed by the heat treatment of hemoglobin below 600 °C. The formation behavior of the pyropolymer was examined by thermogravimetry and differential thermal analysis, and the pyropolymer was characterized by elemental analysis and its 13C nuclear magnetic resonance spectrum. The pyropolymer formation began around 200 °C, and aromatic carbon developed with an increase in the heat-treatment temperature through transformation of the aliphatic carbon in hemoglobin. A noble-metal-free cathode catalyst for a polymer electrolyte fuel cell (PEFC) was formed by heat treatment of the hemoglobin pyropolymer in flowing Ar containing 10% CO2. The activity of the catalyst was dependent on the characteristics of the pyropolymer. The carbon matrix developed with an increase in the aromatic carbon, whereas the micropore development was suppressed. The highest activity was observed for the catalyst with the maximized micropore development. The PEFC using the catalyst with the highest activity obtained in this study generated 0.12 and 0.23 W cm-2 at O2 partial pressures of 54 and 254 kPa, respectively. Continuous PEFC operations and measurements of the extended X-ray absorption fine structures demonstrated that the current decrease during the operation correlated with the structure of the active site of the catalyst

Defect Chemistry in Layered Li<i>M</i>O₂ (<i>M</i> = Co, Ni, Mn, and Li_1/3Mn_2/3) by First-Principles Calculations

The defect chemistry in a series of layered lithium transition-metal oxides, Li<i>M</i>O₂ (<i>M</i> = Co, Ni, Mn, and Li_1/3Mn_2/3), is investigated by systematic first-principles calculations. The calculations clearly show that Ni³⁺ ions in LiNiO₂ are easily reduced, whereas Mn³⁺ ions in LiMnO₂ are easily oxidized under ordinary high-temperature synthesis conditions. It is expected that LiCoO₂ and Li­(Li_1/3Mn_2/3)­O₂ with low defect concentrations are easily synthesized. These results are highly consistent with the characteristics and conductive properties of the oxides observed in experiments. The calculations also suggest that the surfaces of the oxides are reduced at a nanometer scale by immersion of the samples in organic electrolytes of lithium-ion batteries, and the tendency of the surface reduction is consistent with the defect chemistry at high temperatures. The formation of the lithium vacancy and interstitial are elementary reactions of electrode active materials in the charging and discharging processes of lithium-ion batteries, respectively. The defect formation energies in conjunction with the electrode potentials can quantitatively describe the electrode behavior

Water Oxidation through Interfacial Electron Transfer by Visible Light Using Cobalt-Modified Rutile Titania Thin-Film Photoanode

TiO2 is a good photoanode material for water oxidation to form O2; however, UV light (λ < 400 nm) is necessary for this system to operate. In this work, cobalt species were introduced onto a rutile TiO2 thin film grown on a fluorine-doped tin oxide (FTO) substrate for visible-light activation of TiO2 and to construct water oxidation sites. TiO2 thin films were prepared on the FTO surface by the thermohydrolysis of TiCl4, followed by annealing at 723 K in air; the loading of the cobalt species was achieved simply by immersing TiO2/FTO into an aqueous Co­(NO3)2 solution at room temperature, followed by heating at 423 K in air. Physicochemical analyses revealed that the cobalt species deposited on the TiO2 film was α-Co3(OH)4(NO3)2 and that the cobalt-modified TiO2 thin-film electrode had a visible-light absorption band that extended to 700 nm due to interfacial electron transitions from the cobalt species to the conduction band of TiO2. Upon anodic polarization in the presence of visible light, the cobalt-modified TiO2 thin-film electrode generated an anodic photocurrent with an onset potential of +0.1 V vs RHE, which was consistent with that of pristine rutile TiO2. Product analysis during the controlled potential photoelectrolysis in the presence of an applied bias smaller than 1.23 V under visible light showed that water oxidation to O2 occurred on the cobalt-modified TiO2/FTO. This study demonstrates that a visible-light-driven photoelectrochemical cell for water oxidation can be constructed through the use of earth-abundant metals without the need for a complicated preparation procedure