Cell designs for the electrochemical reduction of CO 2 from gas phase were developed and investigated, and the critical elements for an efficient process were identified. Various types of polymeric membrane were used to build membrane electrode assembly adapted for CO 2 reduction in gas phase: protonic and anion exchange membrane (AEM), bipolar membrane and a modified bipolar like membrane configuration. Configurations using anion exchange ionomer in the cathodic catalytic layer in contact with an AEM allow for a great enhancement of the cathode reaction selectivity toward CO. However, a severe problem was identified when co-electrolysis is performed using only an AEM: this type of membrane acts as a CO 2 "pump" meaning that for each molecule of CO 2 reduced at the cathode, one or two CO 2 molecules are produced at the anode by oxidation of the carbonate/bicarbonate anion transported in the membrane. A bipolar membrane system was shown to soften this problem, but only a newly developed cell design was able to fully prevent the parasitic CO 2 pumping. Using this new cell configuration, the faradaic efficiency of an alkaline environment is maintained, the parasitic CO 2 pumping to the anode side is completely suppressed, and the overall cell voltage efficiency is highly improved.

An electrochemical three-electrode flow-cell is presented for in situ small-angle X-ray scattering (SAXS) and X-ray absorption spectroscopy (XAS) experiments in transmission mode at synchrotron X-ray sources. The cell also allows for in situ XAS performed in fluorescence mode. Constant experimental conditions, even under moderate gas evolution, are provided by the electrolyte flow with controlled gas saturation. A special configuration of working and counter electrode, respectively, yields low residual ohmic resistance in three-electrode measurements that enables the study of thick porous electrodes of active high surface area materials. The cell proved its functionality and reliability in two studies: First, an in situ anomalous SAXS experiment for the high-potential degradation properties of a Pt/IrO 2 -TiO 2 catalyst for the oxygen reduction reaction at polymer electrolyte fuel cell cathodes; and second, an in situ XAS study of the electronic state of Ir centers inside an IrO 2 -TiO 2 catalyst under oxygen evolution conditions. © The Author Modern research in electrocatalysis makes extensive use of in situ X-ray techniques that provide information about the structure and the electronic state of catalyst materials under electrochemical potential control. The reason for this is the limited, merely indirect information about the state of the catalyst that can be deduced from purely electrochemical testing like cyclic voltammetry (CV) which often does not allow for an unambiguous interpretation of the data. In order to develop an understanding at a more fundamental level, additional information is required about the potential-dependent state of electrocatalyst materials that can be provided by synchrotron-based techniques like X-ray scattering or X-ray absorption spectroscopy.One example is the investigation of polymer electrolyte fuel cell (PEFC) Pt cathode catalyst degradation. Different mechanisms have been proposed for the loss of electrochemically active Pt surface area (ECSA) that occurs most severely at transient high-potential spikes during PEFC start and stop.1,2 Processes like agglomeration of primary Pt particles due to migration or carbon support corrosion, Pt loss due to dissolution, and growth of primary Pt nanoparticles due to dissolution/redeposition cycles have been considered 3,4 and quantified for different operation conditions and electrochemical environments. The most common technique applied for this purpose is transmission electron microscopy (TEM), which has the convenient advantage that changes of the Pt nanoparticle structure can be directly visualized, especially with the use of identical location TEM (IL-TEM).5 Although successfully demonstrated, 6 in situ TEM remains limited to certain electrochemical systems. Whereas the strength of TEM lies in the direct imaging of individual catalyst particles, it is challenging to extract quantitative statistical information about the entire catalyst sample from TEM analysis. Finally, the distinction of Pt nanoparticles from the support material p...

Our progressive transition from a society energetically dependent on fossil fuels towards one relying on renewable sources requires novel, environmentally friendly energy conversion and storage concepts. Hydrogen is widely regarded as an energy carrier that could circumvent this need, particularly in sight of the foreseeable spread of fuel cell cars that would use this "renewable H 2 ". The latter would be produced using electrolyzers, which in their better established form cannot fulfill the targeted H 2-price due to the low current densities (< 0.5 mA•cm geom-2) associated to their liquid electrolyte. Alternatively, devices based on proton-and anion-exchange membranes are currently under development, and a new kind of co-electrolysis cell in which CO 2 is reduced into hydrocarbons is also envisaged. Electrocatalysts play a crucial role in all of these systems, but the interplay between their surface and the reaction medium (in the so-called interface) is often overlooked in the quest towards better performance. With this motivation, this review discusses the current knowledge of the interfacial catalysis of the three (co-)electrolysis relevant reactions (i.e., the evolution of H 2 and O 2 , and the reduction of CO 2). From this, we identify pH and surface oxidation state as the key electrolyte-and surface-related parameters for which further understanding could lead to improved kinetics, and propose strategies for the tentative design of better electrocatalysts.

Operando X-ray techniques allow an unprecedented, quantitative discrimination of the instability mechanisms affecting Ir-oxide catalysts for the evolution of oxygen.

This work focuses on the performance and stability of selected commercial carbon electrode materials before and after heat-treatment in an operating all-vanadium redox flow battery (VRB). Heat treatment results in improved cell performance for all tested materials, with SGL 39 AA carbon papers and SIGRACELL GFD4.6 EA carbon felt showing the best performance. Further investigation of these two materials by in situ reference electrode measurements reveal improvements after heat-treatment that originate mainly from the negative electrode or V 2+ /V 3+ side of the cell. Upon extended cycling, carbon felt is found to be stable. Carbon papers however, show significant performance losses originating from the negative electrode side. The potential limit during charging and the exposure to very negative potentials appears to be a critical issue at the negative electrode in the VRB. Analysis of both materials after cycling by scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy reveal significant differences in their surface chemistry, structure and morphology. These differences give valuable insights into the behavior and degradation of different carbon materials used in VRBs. Redox flow batteries (RFBs) are a promising technology for efficient energy storage and grid stabilization.1,2 The all-vanadium redox flow battery (VRB), which uses vanadium ions in different oxidation states at the positive and negative electrodes, is the most advanced RFB to date.3 The electrodes are a crucial component of the VRB, as they provide the surface on which the respective electrochemical reactions occur. Thus, catalytic activity, wettability and mass transport properties of the electrodes strongly affect VRB performance. Ideal electrodes for the VRB should provide both: long term durability and stable catalytic activity. Various materials have been considered as electrodes for the use in VRBs including non-carbon based dimensionally stable anode electrodes and carbon based electrodes such as carbon felt, carbon paper, carbon nanotubes, carbon nanofibers or graphene oxides. 4 To enhance electrochemical activity and wettability of carbon based materials in VRBs, different surface modification methods have been used. Carbon electrodes have been coated with metals such as iridium, 5 doped with nitrogen 6 or decorated with nanomaterials such as graphene-nanowalls 7 or graphite carbon nanotubes. Most of these surface treatment approaches introduce functional groups, commonly oxygen onto the carbon electrode surface. This leads to increased wettability and redox activity, which is generally attributed to the increased concentration of surface-active oxygen functional groups.11 Among the various surface modifications, heattreatment is still regarded as the most common and facile approach to incorporate oxygen groups onto the surface of carbon materials. 4 In an effort to better understand the role of oxygen functional groups on electrode performance, Fink et al. studied pristine and heat-treated Rayon (a regene...