Solar water splitting provides a promising path for sustainable hydrogen production and solar energy storage. One of the greatest challenges towards large-scale utilization of this technology is reducing the hydrogen production cost. The conventional electrolyser architecture, where hydrogen and oxygen are co-produced in the same cell, gives rise to critical challenges in photoelectrochemical water splitting cells that directly convert solar energy and water to hydrogen. Here we overcome these challenges by separating the hydrogen and oxygen cells. The ion exchange in our cells is mediated by auxiliary electrodes, and the cells are connected to each other only by metal wires, enabling centralized hydrogen production. We demonstrate hydrogen generation in separate cells with solar-to-hydrogen conversion efficiency of 7.5%, which can readily surpass 10% using standard commercial components. A basic cost comparison shows that our approach is competitive with conventional photoelectrochemical systems, enabling safe and potentially affordable solar hydrogen production.

The notorious instability of non-precious-metal catalysts for oxygen reduction and evolution is by far the single unresolved impediment for their practical applications. We have designed highly stable and active bifunctional catalysts for reversible oxygen electrodes by oxidative thermal scission, where we concurrently rupture nitrogen-doped carbon nanotubes and oxidize Co and Mn nanoparticles buried inside them to form spinel Mn-Co oxide nanoparticles partially embedded in the nanotubes. Impressively high dual activity for oxygen reduction and evolution is achieved using these catalysts, surpassing those of Pt/C, RuO2, and IrO2 and thus raising the prospect of functional low-cost, non-precious-metal bifunctional catalysts in metal-air batteries and reversible fuel cells, among others, for a sustainable and green energy future.

We report here the plasma-enhanced chemical vapor deposition and electrocatalytic characterization of pure NiO x and NiO x (OH) y . Whereas NiO x is deposited if oxygen is used as a reactive gas, the use of air as a reactive gas leads to the deposition of the NiO x (OH) y , which is electrochemically more active than the NiO x . By recording X-ray photoelectron spectra from the as-deposited catalysts and after their electrochemical investigations, we determined that the electrochemical activity correlates with the amount of hydroxide sites on the surface. Such a behavior was already observed for CoO x and CoO x (OH) y . As a consequence, CoNiO x (OH) y was deposited using air as a reactive gas to study the influence of nickel on the electronic structure of CoO x (OH) y and its effect on the electrochemical activity.

To reduce energy losses in water electrolysers a fundamental understanding of the water oxidation reaction steps is necessary to design efficient oxygen evolution catalysts. Here we present CoOx/Ti electrocatalytic films deposited by thermal and plasma enhanced chemical vapor deposition (CVD) onto titanium substrates. We report electrochemical (EC), photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) measurements. The electrochemical behavior of the samples was correlated with the chemical and electronic structure by recording XPS spectra before and after each electrochemical treatment (conditioning and cyclovoltammetry). The results show that the electrochemical behavior of CoOx/Ti strongly depends on the resulting electronic structure and composition. The thermal deposition leads to the formation of a pure Co(II)Ox which transforms to a mixed Co(II)Co(III)Ox during the OER. This change in oxidation state is coupled with a decrease in overpotential from η = 0.57 V to η = 0.43 V at 5 mA cm(-2). Plasma deposition in oxygen leads to a Co(III)-dominated mixed CoOx, that has a lower onset potential as deposited due to a higher Co(III) content in the initial deposited material. After the OER XPS results of the CoOx/Ti indicate a partial formation of hydroxides and oxyhydroxides on the oxide surface. Finally the plasma deposition in air, results in a CoOxOH2 surface, that is able to completely oxidizes during OER to an oxyhydroxide Co(III)OOH. With the in situ formed CoOOH we present a highly active catalyst for the OER (η = 0.34 at 5 mA cm(-2); η = 0.37 V at 10 mA cm(-2)).

Please cite this article as: T. Lostak, S. Krebs, A. Maljusch, T. Gothe, M. Giza, M. Kimpel, J. Flock, S. Schulz, Formation and characterization of Fe 3+ -/Cu 2+ -modified zirconium oxide conversion layers on zinc alloy coated steel sheets, Electrochimica Acta (2013), http://dx. AbstractZirconium oxide conversion layers are considered as environmentally friendly alternatives replacing chromate-based passivation layers in the coil-coating industry. Based on excellent electronic barrier properties they provide an effective corrosion protection of the metallic substrate. In this work, thin layers were grown on HDG-steel-substrates by increasing the local pH at the surface and were characterized using potentiodynamic polarization technique.The influence of Cu(NO 3 ) 2 3H 2 O or Fe(NO 3 ) 3 9H 2 O on morphology and thickness of deposited protective layers were investigated by XPS, ToF-SIMS and FE-SEM. A significant film thickness increase was found by adding Cu 2+ or Fe 3+ ions to the conversion solution. In addition, growth kinetics were studied by in-situ measurements of corrosion potential using potentiodynamic polarization technique.

Simultaneous acquisition of electrochemical impedance spectroscopy and quartz crystal microbalance (EIS-EQCM) data in cyclic electrode potential scans was used to characterize nonstationary underpotential deposition (UPD) of atomic layers of Ag on Au and Cu on Pt. Both EIS and EQCM data sets complemented each other in the elucidation of interface models and the investigation of different aspects of the interfacial dynamics. EIS-EQCM provided an opportunity to monitor coadsorption and competitive adsorption of anions during the Ag and Cu UPD using (i) the electrode mass change, (ii) adsorption capacitances, and (iii) double-layer capacitances. Kinetic information is available in the EIS-EQCM through the charge transfer resistances and apparent rate coefficients. The latter expresses the rate of UPD into the partially covered electrode surface. The apparent rate coefficients for the Ag UPD were determined to vary from 0.15 to 0.45 cm/s which is between the standard constant rates k 0 of Ag bulk deposition on Ag reported previously for different Ag surfaces. Cu UPD on Pt and Ag UPD on Au contributed differently into a resonance resistance ΔR(E) available from the EQCM data sets. Spontaneous surface alloying between Ag and Au during the Ag UPD continuously increased the ΔR, while the Cu overlayer formation on Pt as well as experiments without Ag þ and Cu 2þ in the solution did not change this parameter significantly. The EIS-EQCM appeared to be a promising tool for an improved characterization and understanding of nonstationary electrochemical interfaces.

The solid electrolyte interphase (SEI) is an electronically insulating film formed from the decomposition of the organic electrolyte at the surface of the negative electrodes in Li‐ion batteries (LIBs). This film is of vital importance in the performance and safety of LIBs. Atomic force microscopy (AFM) and scanning electrochemical microscopy (SECM) are combined in one platform for the consecutive in situ investigation of surface reactions in LIBs inside an Ar‐filled glovebox. As proof of concept, the formation and the electrochemical properties of the SEI formed on glassy carbon electrodes are investigated. Changes in topography during film formation of the SEI are studied via AFM. The AFM tip is then used to partially remove a small area (50×50 μm2) of the SEI, which is subsequently probed using SECM in feedback mode. The AFM‐scratched spot is clearly visualized in the SECM image, demonstrating the strength of the AFM/SECM combination for the investigation in the field of LIBs.

Acquisition of localized electrochemical impedance spectra as a function of spatial coordinates combined with novel approaches of data analysis brings a key for visualization of two-dimensional distributions of important parameters describing solid/liquid interfaces. They include the capacitance of the electric double layer, the resistance of the interfacial charge transfer, capacitances of adsorption, or other parameters depending on the properties of the system. Additionally, the proposed approach eliminates many common methodological problems of localized electrochemical impedance microscopies related to the frequency dependence of the actual pictures and difficulties with raw data interpretation. Thus, it offers a unique insight into the localized processes at the interface which is not possible to achieve using classical techniques.