A hydrogen generator coupled to a hydrogen heater for small scale portable applications

This study aims to build and test a small scale portable device able to couple a hydrogen generation system (based on a NaBH4 solution as liquid H2 carrier) to a hydrogen heater (based on the exothermic catalytic combustion of the released H2). The hydrogen generating system is based on the hydrolysis of stabilized solutions of NaBH4 (fuel solutions) which are pumped into the hydrolysis reactor. The generated H2 feeds the catalytic combustor. Two catalysts have been developed for the H2 generation and the combustion reactions able to operate at room temperature without need of additional energy supply. For the NaBH4 hydrolysis a Co-B catalyst was supported on a perforated and surface treated stainless steel (SS316) home-made monolith. For the flameless H2 catalytic combustion a Pt catalyst was prepared on a commercial SiC foam. The device was automatized and tested for the on-demand production of heat at temperatures up to 100ºC. In steady state conditions the NaBH4 solution flow is controlling the H2 flux and therefore the heater temperature. Once the steady-state is reached the system responds in a few minutes to up and down temperature demands from 80 to 100 ºC. The catalysts have shown no deactivation during the tests carried out in several days.

Microstructural Investigation and On-Site Repair of Thin Pd-Ag Alloy Membranes

Pd membranes act in an important role in H2 purification and H2 production in membrane reactors. Pd-Ag alloy membranes fabricated by consecutive electroless- and electroplating process on alumina tubes exhibited good stability under stringent heating/cooling cycles at a ramp rate of 10 K/min, imitating practical fast initiation or emergency shutdown conditions. Bilayer Pd-Ag membranes can form dense and uniform alloy after thermal treatment for 24 h at 823 K under H2 atmosphere, despite a porous structure due to the development of liquid-like properties above Tamman temperature to enforce the migrativity. On the contrary, alloying under N2 atmosphere resulted in a Pd-enriched layer. This led to a lower H2 flux but superior thermal stability compared to that alloying under H2 atmosphere. The trilayer approach of electroless-plated Pd, electro-polated Ag and electroless-plated Pd is not suitable to achieve homogeneous Pd-Ag alloys, which, on the other hand, presented the occurrence of a small gap between top Pd layer and middle Ag layer, probably due to insufficient wetting during plating process. An on-site repair treatment in analogous to MOCVD (Metal-organic Chemical Vapor Deposition) process was first proposed to extend the lifetime of Pd-Ag membrane, i.e., by vaporizing, and subsequent decomposition of Ag(OOCC2F5) powders to “preferentially” block the pinholes under vacuum and at working temperature of ca. 473–673 K, which effectively reduced the N2 flux by 57.4% compared to the initial value. The H2 flux, however, declined by 16.7% due to carbon deposition on the membrane surface, which requires further investigation. This approach shows some potential for on-site repair without disassembly or cooling to room temperature.

Hydrogen Purification from Compact Palladium Membrane Module Using a Low Temperature Diffusion Bonding Technology

This study investigates a compact palladium membrane module (CPMM) for hydrogen purification, assembled by diffusion bonding at a low-temperature (450 °C). This CPMM resulted in hydrogen (H2) flux of 18.3 mL cm−2 min−1 with H2/N2 selectivity of over 1100. The H2 purification test using a 60% H2/40% CO2 mixed gas confirmed that the CPMM can separate H2 with a concentration of more than 99%, with a pressure difference of 5 bar. Moreover, the volume of the diffusion bonded membrane module is decreased by 81.4% than the flame-type membrane module pre-studied in our laboratory.

Short- and long-term near-infrared spectroscopic variability of eruptive protostars from VVV

ABSTRACT Numerous eruptive variable young stellar objects (YSOs), mostly Class I systems, were recently detected by the near-infrared Vista Variables in the Via Lactea (VVV) survey. We present an exploratory near-infrared spectroscopic variability study of 14 eruptive YSOs. The variations were sampled over one-day and one-to-two-year intervals and analysed in combination with VVV light curves. CO overtone absorption features are observed on three objects with FUor-like spectra: all show deeper absorption when they are brighter. This implies stronger emission from the circumstellar disc with a steeper vertical temperature gradient when the accretion rate is higher. This confirms the nature of fast VVV FUor-like events, in line with the accepted picture for classical FUors. The absence of Brγ emission in a FUor-like object declining to pre-outburst brightness suggests that reconstruction of the stellar magnetic field is a slow process. Within the one-day time-scale, 60 per cent of H2-emitting YSOs show significant but modest variation, and 2/6 sources have large variations in Brγ. Over year-long time-scales, H2 flux variations remain modest despite up to 1.8 mag variation in Ks. This indicates that emission from the molecular outflow usually arises further from the protostar and is unaffected by relatively large changes in accretion rate on year-long time-scales. Two objects show signs of on/off magnetospheric accretion traced by Brγ emission. In addition, a 60 per cent inter-night brightening of the H2 outflow is detected in one YSO.

A new estimation of the recent tropospheric molecular hydrogen budget using atmospheric observations and variational inversion

This paper presents an analysis of the recent tropospheric molecular hydrogen (H2) budget with a particular focus on soil uptake and European surface emissions. A variational inversion scheme is combined with observations from the RAMCES and EUROHYDROS atmospheric networks, which include continuous measurements performed between mid-2006 and mid-2009. Net H2 surface flux, then deposition velocity and surface emissions and finally, deposition velocity, biomass burning, anthropogenic and N2 fixation-related emissions were simultaneously inverted in several scenarios. These scenarios have focused on the sensibility of the soil uptake value to different spatio-temporal distributions. The range of variations of these diverse inversion sets generate an estimate of the uncertainty for each term of the H2 budget. The net H2 flux per region (High Northern Hemisphere, Tropics and High Southern Hemisphere) varies between −8 and +8 Tg yr−1. The best inversion in terms of fit to the observations combines updated prior surface emissions and a soil deposition velocity map that is based on bottom-up and top-down estimations. Our estimate of global H2 soil uptake is −59±9 Tg yr−1. Forty per cent of this uptake is located in the High Northern Hemisphere and 55% is located in the Tropics. In terms of surface emissions, seasonality is mainly driven by biomass burning emissions. The inferred European anthropogenic emissions are consistent with independent H2 emissions estimated using a H2/CO mass ratio of 0.034 and CO emissions within the range of their respective uncertainties. Additional constraints, such as isotopic measurements would be needed to infer a more robust partition of H2 sources and sinks.