The hydrogen evolution reaction (HER) is a crucial electrochemical process for the proposed hydrogen economy since it has the potential to provide pure hydrogen for fuel cells. Nowadays, hydrogen electroproduction is considerably expensive, so promoting the development of new non-noble catalysts for the cathode of alkaline electrolyzers appears as a suitable way to reduce the costs of this technology. In this sense, a series of tungsten-based carbide materials have been synthesized by the urea-glass route as candidates to improve the HER in alkaline media. Moreover, two different pyridinium-based ionic liquids were employed to modify the surface of the carbide grains and control the amount and nature of their surface species. The main results indicate that the catalyst surface composition is modified in the hybrid materials, which are then distinguished by the appearance of tungsten suboxide structures. This implies the action of ionic liquids as reducing agents. Consequently, differential electrochemical mass spectrometry (DEMS) is used to precisely determine the onset potentials and rate-determining steps (RDS) for the HER in alkaline media. Remarkably, the modified surfaces show high catalytic performance (overpotentials between 45 and 60 mV) and RDS changes from Heyrovsky-Volmer to Heyrovsky as the surface oxide structures get reduced. H₂O molecule reduction is then faster at tungsten suboxide, which allows the formation of the adsorbed hydrogen at the surface, boosting the catalytic activity and the kinetics of the alkaline HER.

Pt-Ru nanoparticles supported on carbon nanofibers (CNF) were synthesized by the sodium borohydride reduction method, using different generation dendrimers (zero, one, two and three generations). After the synthesis process, these materials were submitted to a heat treatment at 350 °C, in order to clean the nanoparticle surface of organic residues. TEM characterization showed that the Pt-Ru nanoparticles size ranged between 1.9 and 5.5 nm. The use of dendrimers did not totally avoid the formation of aggregates, although monodisperse sizes were observed. The heat treatment produces the desired surface cleaning, although promoted the formation of agglomerates and crystalline Ru oxides. The study of the electrochemical activity towards the methanol oxidation displayed some clues about the influence of both the dendrimer generation and the presence of Ru oxides. Moreover, the apparent activation energy E_ap for this reaction was determined. The results showed a beneficial effect of the heat treatment on the methanol oxidation current densities for the materials synthesized with the biggest dendrimers, being the methanol deprotonation and CO_ad diffusion the predominant rate determining steps (rds).

Ni nanoparticles supported on graphene-based materials were tested as catalysts for the oxygen reduction reaction (ORR) to be used in anion exchange membrane fuel cells (AEMFCs). The introduction of N into the graphene structure produced an enhancement of electrocatalytic activity by improving electron transfer and creating additional active sites for the ORR. Materials containing both N and S demonstrated the highest stability, showing only a 3% performance loss after a 10 h stability test and therefore achieving the best overall performance. This long-term durability is attributed to the synergetic effect of Ni nanoparticles and bi-doped (S/N)-reduced graphene oxide. The findings suggest that the strategic incorporation of both nitrogen and sulphur into the graphene structure plays a crucial role in optimising the electrocatalytic properties of Ni-based catalysts.

On 19 September 2021, the largest historic eruption of La Palma began, named the Tajogaite volcano. It was active for 85 days, ending on 13 December 2021. During eruptions, the exposure to natural pollutants rises above background levels due to gas emissions and particulate matter (ash and aerosols) into the atmosphere. Moreover, rock fracturing due to magma injection and seismic activity associated with the eruptive phenomena can increase the ground permeability, having a potential effect on radon (222Rn) emissions. During the eruptive and post-eruptive period of the Tajogaite volcano, 222Rn measurements were performed across the affected areas to assess the possible radiological impact of this volcanic episode on La Palma inhabitants.During the first weeks of the eruption, 88 Solid State Nuclear Track (CR-39-SSNT) detectors were deployed at workplaces and dwellings, mainly located in the vicinity of the eruption, though several detectors were also placed in more distant areas for comparison. These detectors were exposed for ca. 90 days, from September 2021 to January 2022, though only 77 detectors could be retrieved as the rest were buried by the lavas. In addition, 3 portable RadonScout devices (SARAD GmbH) were used for continuous monitoring (1 h integration time) of radon and environmental parameters (air temperature, humidity and barometric pressure). They were installed inside 3 buildings located 2.8-5 km from the volcano.Eighty percent of the CR-39-SSNT radon data were below the reference level of 300 Bq/m3 (Directive 2013/59/Euratom). Of the remaining detectors, a large percentage of radon levels were above 300 Bq/m3 in the Aridane valley, an area close to the volcano, and with a clear spatial pattern showing higher levels of 222Rn at shorter distances to the eruptive centre. Continuous monitoring of radon showed low 222Rn levels (< 300 Bq/m3) at the two sites furthest from the volcano, with fluctuations highly correlated with environmental variables. Several anomalies of 222Rn reaching up to 4000 Bq/m3 were detected during the eruptive period in the monitoring station located closer to the eruptive centre, unrelated to the observed environmental variables. These anomalies were synchronous with the occurrence of large explosive events and phreatomagmatic pulses during the eruption.The computed effective dose due to the contribution of 222Rn during the 3 months of eruption was 0.3 mSv, which, extrapolated to the annual reference value, provides an estimated effective dose of 0.9 mSv/year. This value is 50% lower than the estimated worldwide annual average dose from natural and artificial radiation sources (2.4 mSv/year) (UNSCEAR 2000). Thus, radon levels during the Tajogaite eruption did not lead to a significant increase in exposure level to this radioactive gas. However, transient radon bursts have been recorded associated with several phases of the volcanic activity. AcknowledgmentsThis study was supported by the Spanish Ministry of Science and Innovation (BOE-A-2021-20262).References:Council Directive 2013/59/Euratom laying down basic safety standards for protection against the dangers arising from exposure to ionising radiation, and repealing Directives 89/618/Euratom, 90/641/Euratom, 96/29/Euratom, 97/43/Euratom and 2003/122/Euratom.UNSCEAR (2000), Sources and effects of ionizing radiation. UNITED NATIONS, New York.

Oxygen reduction reaction (ORR) is one of the key features for the efficient functioning of several energy conversion devices such as fuel cells, appearing the necessity of development of new low-cost catalyst materials. Carbon-doped materials have attracted attention in this field due to its physicochemical and electronic properties. In this work, a nitrogen and sulfur doped material with anchored Co3O4 nanoparticles (Co/SN-rGO) is proposed as cathode catalyst for direct ethanol fuel cells (DEFCs) and results are compared with graphene nanomaterials (GMs) synthesized using graphene oxide as precursor. The effect of the heteroatoms and cobalt nanoparticles in the final efficiency was studied. Synthesized materials were characterized and the activity of Co/SN-rGO and GMs against ORR was studied. Co/SN-rGO performance in a DEFC was also evaluated using a fuel cell test station. Main results indicate higher catalytic activity, stability, and ethanol tolerance of Co/SN-rGO in comparison to a carbon-supported Pt catalyst.