Compound materials, such as transition-metal (TM) carbides, are anticipated to be effective electrocatalysts for the carbon dioxide reduction reaction (CO 2 RR) to useful chemicals. This expectation is nurtured by density functional theory (DFT) predictions of a break of key adsorption energy scaling relations that limit CO 2 RR at parent TMs. Here, we evaluate these prospects for hexagonal Mo 2 C in aqueous electrolytes in a multimethod experiment and theory approach. We find that surface oxide formation completely suppresses the CO 2 activation. The oxides are stable down to potentials as low as −1.9 V versus the standard hydrogen electrode, and solely the hydrogen evolution reaction (HER) is found to be active. This generally points to the absolute imperative of recognizing the true interface establishing under operando conditions in computational screening of catalyst materials. When protected from ambient air and used in nonaqueous electrolyte, Mo 2 C indeed shows CO 2 RR activity.

The hydrogen evolution reaction (HER) has been crucial for the development of fundamental knowledge on electrocatalysis and electrochemistry, in general. In alkaline media, many key questions concerning pH-dependent structure–activity relations and the underlying activity descriptors remain unclear. While the presence of Ni(OH) 2 deposited on Pt(111) has been shown to highly improve the rate of the HER through the electrode’s bifunctionality, no studies exist on how low coverages of Ni(OH) 2 influence the electrocatalytic behavior of Cu surfaces, which is a low-cost alternative to Pt. Here, we demonstrate that Cu(111) modified with 0.1 and 0.2 monolayers (ML) of Ni(OH) 2 exhibits an unusual non-linear activity trend with increasing coverage. By combining in situ structural investigations with studies on the interfacial water orientation using electrochemical scanning tunneling microscopy and laser-induced temperature jump experiments, we find a correlation between a particular threshold of surface roughness and the decrease in the ordering of the water network at the interface. The highly disordered water ad-layer close to the onset of the HER, which is only present for 0.2 ML of Ni(OH) 2 , facilitates the reorganization of the interfacial water molecules to accommodate for charge transfer, thus enhancing the rate of the reaction. These findings strongly suggest a general validity of the interfacial water reorganization as an activity descriptor for the HER in alkaline media.

The electrocatalytic behavior of a tungsten carbide-supported Pt(3 wt %)Au(3 wt %)Sn(10 wt %) catalyst (PtAuSn/W 2 C) is investigated toward the oxidation of ethanol at temperatures below 70 °C. Vulcan XC-72-supported Pt(3 wt %)Au(3 wt %)Sn(10 wt %) is used as a reference (PtAuSn/C). For a better understanding of the reaction mechanism, in situ techniques such as electrochemical mass spectrometry (EC-MS) and Fourier transform infrared spectroscopy (FTIRS) are employed. We show that PtAuSn/W 2 C has a higher electrocatalytic performance than PtAuSn/C, with a CO 2 conversion efficiency of 6.5% detected at 0.65 V versus the reversible hydrogen electrode (RHE) at room temperature with on-line quantitative EC-MS measurements. FTIR spectra analysis and EC-MS during the ethanol oxidation reaction (EOR) show C−C bond breaking at the admission potential (0.05 V RHE ) and an onset potential for the CO 2 formation at E ≥ 0.20 V RHE . The CO tolerance of Pt nanoparticles in PtAuSn/W 2 C is improved by the presence of oxide species on W 2 C through a bifunctional mechanism, as well as the electronic charge transfer from the W 2 C support to the metallic nanoparticles through an electronic effect.

Long term galvanostatic charge/discharge cycling of oxygen deficient, carburized and self‐organized titanium dioxide (TiO2) nanotubes (NTs) in sodium ion (Na) batteries (SIBs) are subject to a significant self‐improving charge storage behavior. Surface reactions upon sodiation of carburized NTs form acicular surface films that can be reversibly cycled. We show that, alongside organic species from the decomposition of the electrolyte, mainly inorganic compounds, such as Na2O2 and Na2CO3, are the main constituents. These components possess a characteristic acicular morphology. Na2O2 is found to form upon sodiation and converted to NaO2 upon desodiation. This, in combination with its pseudo‐capacitive charge storage characteristics, explains the excellent rate capability measured for TiO2‐x‐C NTs. The observed high reversibility of this surface chemistry is also essential for the fast kinetics and the high capacity retention found in the system. Our findings point to a more general Na‐ion storage mechanism, that is potentially relevant to other transition metal oxides also.

Developing sodium (Na)-ion batteries is highly appealing because they offer the potential to be made from raw materials, which hold the promise to be less expensive, less toxic, and at the same time more abundant compared to state-of-the-art lithium (Li)-ion batteries. In this work, the Na-ion storage capability of nanostructured organic−inorganic polyaniline (PANI) titanium dioxide (TiO 2 ) composite electrodes is studied. Self-organized, carbon-coated, and oxygen-deficient anatase TiO 2−x -C nanotubes (NTs) are fabricated by a facile one-step anodic oxidation process followed by annealing at high temperatures in an argon−acetylene mixture. Subsequent electropolymerization of a thin film of PANI results in the fabrication of highly conductive and well-ordered, nanostructured organic−inorganic polyaniline-TiO 2 composite electrodes. As a result, the PANI-coated TiO 2−x -C NT composite electrodes exhibit higher Na storage capacities, significantly better capacity retention, advanced rate capability, and better Coulombic efficiencies compared to PANIcoated Ti metal and uncoated TiO 2−x -C NTs for all current rates (C-rates) investigated.