Active in alkaline environment: The activity of nickel, silver, and copper catalysts for the electrochemical transformation of water to molecular hydrogen in alkaline solutions was enhanced by ...modification of the metal surfaces by Ni(OH)2 (see picture; I=current density and η=overpotential). The hydrogen evolution reaction rate on a Ni electrode modified by Ni(OH)2 nanoclusters is about four times higher than on a bare Ni surface.
The classic models of metal electrode-electrolyte interfaces generally focus on either covalent interactions between adsorbates and solid surfaces or on long-range electrolyte-metal electrostatic ...interactions. Here we demonstrate that these traditional models are insufficient. To understand electrocatalytic trends in the oxygen reduction reaction (ORR), the hydrogen oxidation reaction (HOR) and the oxidation of methanol on platinum surfaces in alkaline electrolytes, non-covalent interactions must be considered. We find that non-covalent interactions between hydrated alkali metal cations M(+)(H(2)O)(x) and adsorbed OH (OH(ad)) species increase in the same order as the hydration energies of the corresponding cations (Li(+) >> Na(+) > K(+) > Cs(+)) and also correspond to an increase in the concentration of OH(ad)-M(+)(H(2)O)(x) clusters at the interface. These trends are inversely proportional to the activities of the ORR, the HOR and the oxidation of methanol on platinum (Cs(+) > K(+) > Na(+) >> Li(+)), which suggests that the clusters block the platinum active sites for electrocatalytic reactions.
The particle size effect on the formation of OH adlayer, the CO bulk oxidation, and the oxygen reduction reaction (ORR) have been studied on Pt nanoparticles in perchloric acid electrolyte. From ...measurements of the CO displacement charge at controlled potential, the corresponding surface charge density versus potential curves yielded the potentials of total zero charge (pztc), which shifts approximately 35 mV negative by decreasing the particle size from 30 nm down to 1 nm. As a consequence, the energy of adsorption of OH is more enhanced, that is, at the same potential the surface coverage with OH increases by decreasing the particle size, which in turn affects the catalytic reactions thereon. The impact of the electronically induced potential shift in the OH adsorption is demonstrated at the CO bulk oxidation, in which adsorbed OH is an educt species and promotes the reaction, and the ORR, where it can act as a surface site blocking species and inhibits the reaction.
This Letter reveals new findings on the influence of noncovalent interactions on the electrochemical interface. Using surface X-ray scattering, we demonstrate that the barium cations are located at ...3.4 Å away from the surface, suggesting that they are partially hydrated, though not adsorbed at the surface. The effect of the cation on the oxygen reduction reaction (ORR) ranges from significant (Pt) to little (Au), depending on the nature of the metal and cation. Finally, we show that these results, as obtained on well-defined single-crystal surfaces, correlate well with observations on high surface area nanoparticle catalysts.
The aim of this report is to scrutinize the thin-film rotating disc electrode (TF-RDE) method for investigating the electrocatalytic activity of high surface area catalysts. Special emphasis is given ...to the oxygen reduction reaction (ORR) on carbon-supported platinum catalysts. On the basis of measurements on four different Pt catalyst samples with various average particle sizes, it is demonstrated in detail how the intrinsic properties of the catalyst, i.e., the mass activity (A/g
Pt) and the specific activity (A/m
2
Pt), are evaluated. The potential sources of error are critically discussed and guidelines for the measurements are given. Furthermore, the specific ORR activities determined for the different catalyst samples are analyzed and compared to polycrystalline Pt. The previously reported effect of the particle size on the specific activity for the ORR is interpreted on the basis of the shift in the potential of zero total charge and the concomitant alteration of the adsorption properties.
•TnC deficiency leads to spontaneous hyperactivity and poor sensorimotor coordination.•EE abolishes hyperactivity and modestly rescues sensorimotor deficits in TnC−/− mice.•TnC deficiency attenuates ...the beneficial effect of EE in reducing acrophobia.•EE reveals lower learning/memory capacity and cognitive inflexibility in TnC−/− mice.•Effect of genetic background on behavioral responses can be altered by housing in EE.
Tenascin-C (TnC) is an extracellular matrix glycoprotein implicated in a variety of processes ranging from brain development to synaptic plasticity in the adult vertebrates. Although the role of the TnC gene in regulation of behavior has been investigated, it remained elusive how TnC deficiency interacts with the environment in shaping the behavioral phenotype. To address this, 3-week-old TnC+/+ and TnC-/- male mice were housed over an 8-week period in standard conditions (SC), or enriched environment (EE). A comprehensive battery of tests was used in behavioral phenotyping. When housed in SC, TnC−/− mice showed spontaneous nocturnal hyperactivity, as well as poor sensorimotor coordination and low swimming velocity. However, housing of TnC−/− mice in EE abolished hyperlocomotion, led to faster habituation to novel environment, strengthened the grasp of fore limbs and partially improved movement coordination, while the swimming ability remained deficient. Conversely, TnC deficiency attenuated both the beneficial effects of EE on learning/memory capacity and the anxiolytic effect of EE in reducing the level of acrophobia. This study expands the existing knowledge about the phenotype associated with TnC deficiency, and reveals that the effect of genetic background on the behavioral response could be altered by post-weaning housing in a highly stimulating environment.
Pt extended surfaces and nanoparticle electrodes are used to understand the origin of anomalous activities for electrocatalytic reactions in alkaline electrolytes as a function of cycling/time. ...Scanning tunneling microscopy (STM) of the surfaces before and after cycling in alkaline electrolytes was used to understand the morphology of the impurities and their impact on the catalytic sites. The nature of the contaminant species is identified as 3d-transition metal cations, and the formation of hydr(oxy)oxides of these elements is established as the main reason for the observed behavior. We find that, while for the oxygen reduction reaction (ORR) and the hydrogen oxidation reaction (HOR) the blocking of the sites by the undesired 3d-transition metal hydr(oxy)oxide species leads to deactivation of the reaction activities, the CO oxidation reaction and the hydrogen evolution reaction (HER) can have beneficial effects from the same impurities, the latter being dependent on the exact nature of the adsorbing species. These results show the significance of impurities present in real electrolytes and their impact on electrocatalysis.
The oxygen reduction reaction (orr) has been studied on carbon supported multimetallic catalysts in aqueous acidic electrolyte. The bimetallic catalysts had the nominal compositions of 50 and 75 at.% ...Pt with the alloying elements being Ni and Co. A ternary catalyst consisted of Pt, Rh and Fe in the ratio of 1:0.3:0.7. Comparison is made to carbon supported Pt. The particle size distribution of the metallic phases was obtained by high resolution transmission electron microscopy (HRTEM). An estimation of the surface composition was obtained from the hydrogen adsorption charge and the particle size. Electrochemical measurements were performed using the thin-film rotating ring-disk electrode (RRDE) method in 0.1 M HClO
4 at 20–60
°C. Kinetic analysis in comparison to pure Pt revealed an activity enhancement (per Pt surface atom) of a factor of 2 to 3 for the 50 at.% Co-catalyst. The 25 at.% Co(Ni) and the ternary catalyst revealed similar activity compared with pure Pt. The 50 at.% Ni catalyst was actually less active than the Pt standard and unstable at oxygen electrode potentials. Ring-current collection measurements for peroxide indicated no significant differences between the alloy catalysts and pure Pt with the exception of the 50 at.% Ni catalyst which had a higher peroxide yield. Comparison was also made to results obtained under equal experimental conditions on polycrystalline (pc) Pt
3Ni and Pt
3Co alloy electrodes. These bulk alloys were prepared in UHV to obtain a well defined surface composition of 75 at.% Pt and 25 at.% Co and Ni, respectively. A Pt(pc) electrode served for comparison. The bulk alloys also have an enhanced activity for the orr by about a factor of 2 versus the identically prepared Pt(pc) electrode.
We describe a comparative study of the oxygen reduction reaction on two carbon-supported Pt-based alloy catalysts in aqueous acidic electrolyte at low temperature. Both alloys have the bulk ...compositions of 50 and 75 at. % Pt, with the alloying elements being Ni and Co. Comparison is made to a pure Pt catalyst on the same carbon support, Vulcan XC-72, having the same metal loading (20 wt %) and nominally the same particle size (4 ± 2 nm). High-resolution electron microscopy was used to determine the size and shape of the particles as well as the particle size distribution on all catalysts. Electrochemical measurements were performed using the thin-film rotating ring−disk electrode method in 0.1 M HClO4 at 20−60 °C. Hydrogen adsorption pseudocapacitance was used to determine the number of Pt surface atoms and to estimate the surface composition of the alloy catalysts. Kinetic analysis in comparison to pure Pt revealed a small activity enhancement (per Pt surface atom) of ca. 1.5 for the 25 at. % Ni and Co catalysts, and a more significant enhancement of a factor of 2−3 for the 50 at. % Co. The 50 at. % Ni catalyst was less active than the Pt standard and unstable at oxygen electrode potentials. Ring-current collection measurements for peroxide indicated no significant differences between the Pt−Co catalysts or the 25 at. % Ni catalyst and pure Pt, while the 50 at. % Ni catalyst had a higher peroxide yield. Together with the observed Tafel slopes and activation energies, it was concluded that the kinetic enhancement is contained in the preexponential factor of the conventional transition state theory rate expression. It is, however, not clear why the alloying with Ni or Co produces this change in the preexponential factor.
