ith the growing importance and falling prices of renewable electricity, the issue of electricity storage to deal with the intermittent nature of renewable energy sources is becoming urgent. Storing renewable electricity in chemical bonds ('electrofuels') is particularly attractive, as it allows for high-energy-density storage and potentially high flexibility. While hydrogen is the most likely and realistic candidate for electricity storage in electrofuels, research on the electrochemical conversion of carbon dioxide and water into carbon-based fuels has intrigued electrochemists for decades, and is currently undergoing a notable renaissance [1][2][3][4] . In contrast to hydrogen production by water electrolysis, carbon dioxide electrolysis is still far from a mature technology. Significant hurdles regarding energy efficiency, reaction selectivity and overall conversion rate need to be overcome if electrochemical carbon dioxide reduction is to become a viable option for storing renewable electricity.Many electrocatalysts have been reported for the production of different compounds from the electrocatalytic carbon dioxide reduction reaction (CO 2 RR). Table 1 gives an overview of some of the most active and selective metal or metal-derived electrocatalysts towards specific products in aqueous media. The two-electron transfer products, CO and HCOOH, can be produced with low overpotential and high Faradaic efficiency on suitable electrocatalysts, but substantially higher overpotentials and lower selectivities are observed for multi-electron transfer products such as methane, ethylene and alcohols 2 . For a recent discussion about the economic perspectives of CO 2 RR, the reader is referred to a previous analysis 5 .The aim of this Review is not to be exhaustive, but rather to selectively (and subjectively) discuss some recent advances and pertinent challenges in this field, focusing on themes that have recently witnessed important progress 2,3,6,7 . An overview of some of the themes covered in this Review is shown in Fig. 1. We also discuss two important methodologies used to increase fundamental understanding of CO 2 RR: in situ spectroscopic techniques and computational techniques.

Carbon dioxide and carbon monoxide can be electrochemically reduced to useful products such as ethylene and ethanol on copper electrocatalysts. The process is yet to be optimized and the exact mechanism and the corresponding reaction intermediates are under debate or unknown. In particular, it has been hypothesized that the C-C bond formation proceeds via CO dimerization and further hydrogenation. Although computational support for this hypothesis exists, direct experimental evidence has been elusive. In this work, we detect a hydrogenated dimer intermediate (OCCOH) using Fourier transform infrared spectroscopy at low overpotentials in LiOH solutions. Density functional theory calculations support our assignment of the observed vibrational bands. The formation of this intermediate is structure sensitive, as it is observed only during CO reduction on Cu(100) and not on Cu(111), in agreement with previous experimental and computational observations.

Understanding the competition between hydrogen evolution and CO2 reduction is of fundamental importance to increase the faradaic efficiency for electrocatalytic CO2 reduction in aqueous electrolytes. Here, by using a copper rotating disc electrode, we find that the major hydrogen evolution pathway competing with CO2 reduction is water reduction, even in a relatively acidic electrolyte (pH 2.5). The mass-transport-limited reduction of protons takes place at potentials for which there is no significant competition with CO2 reduction. This selective inhibitory effect of CO2 on water reduction, as well as the difference in onset potential even after correction for local pH changes, highlights the importance of differentiating between water reduction and proton reduction pathways for hydrogen evolution. In-situ FTIR spectroscopy indicates that the adsorbed CO formed during CO2 reduction is the primary intermediate responsible for inhibiting the water reduction process, which may be one of the main mechanisms by which copper maintains a high faradaic efficiency for CO2 reduction in neutral media.

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The present work focus the study of cortical bone samples of different origins (human and animal) subjected to different calcination temperatures (600, 900 and 1200 8C) with regard to their chemical and structural properties. For that, not only standard techniques such as thermogravimetric analysis, Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy were used but also mercury intrusion porosimetry. The latter technique was applied to evaluate the effects of the temperature on the microstructure of the calcined samples regarding porosity and pore size distribution.Although marked alterations in structure and mineralogy of the bone samples on heating were detected, these alterations were similar for each specimen. At 600 8C the organic component was removed and a carbonate apatite was obtained. At 900 8C, carbonate was no longer detected and traces of CaO were found at 1200 8C. Crystallinity degree and crystallite size progressively increased with the calcination temperature, contrary to porosity that strongly decreased at elevated temperatures. In fact, relatively to the control samples, a significant increase in porosity was found in samples calcined at 600 8C (reaching values around 50%). At higher temperatures, a dramatic decrease was observed, reaching, at 1200 8C, values comparable to those of the non-calcined bone. #

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The present work focuses on the physicochemical characterization of selected mineral-based biomaterials that are frequently used in dental applications. The selected materials are commercially available as granules from different biological origins: bovine, porcine, and coralline. Natural and calcined human bone were used for comparison purposes. Besides a classical rationalization of chemical composition and crystallinity, a major emphasis was placed on the measurement of various morphostructural properties such as particle size, porosity, density, and specific surface area. Such properties are crucial to acquiring a full interpretation of the in vivo performance. The studied samples exhibited distinct particle sizes (between 200 and 1000 lm) and shapes. Mercury intrusion revealed not only that the total sample porosity varied considerably (33% for OsteoBiol 1 , 50% for PepGen P-15 1 , and 60% for BioOss 1 ) but also that a significant percentage of that porosity corresponded to submicron pores. Biocoral 1 was not analyzed by this technique as it possesses larger pores than those of the porosimeter upper limit. The density values determined for the calcined samples were close to the theoretical values of hydroxyapatite. However, the values for the collagenated samples were lower, in accordance with their lower mineral content. The specific surface areas ranged from less than 1 m 2 /g (Biocoral) up to 60 m 2 /g (BioOss). The chemical and phase composition of most of the samples, the exception being Biocoral (aragonite), were hydroxyapatite based. Nonetheless, the samples exhibited different organic material content as a consequence of the distinct heat treatments that each had received. '