A comparison of hydrogen storage technologies for solar-powered stand-alone power supplies: A photovoltaic system sizing approach

This paper compares the performance of three different solar based technologies for a stand-alone power supply (SAPS) using different methods to address the seasonal variability of solar insolation—(i) photovoltaic (PV) panels with battery storage; (ii) PV panels with electrolyser and hydrogen (_H2)$({\mathrm{H}}_2)$ storage; and (iii) photoelectrolytic (PE) dissociation of water for _H2${\mathrm{H}}_2$ generation and storage. The system size is determined at three different Australian locations with greatly varying latitudes—Darwin (12^°S${12}^{°}\mathrm{S}$), Melbourne (38^°S${38}^{°}\mathrm{S}$) and Macquarie Island (55^°S${55}^{°}\mathrm{S}$). While the PV/electrolyser system requires fewer PV panels compared to the PV/battery scenario due to the seasonal storage ability of _H2${\mathrm{H}}_2$, the final number of PV modules is only marginally less at the highest latitude due to the lower energy recovery efficiency of _H2${\mathrm{H}}_2$ compared to batteries. For the PE technology, an upper limit on the cost of such a system is obtained if it is to be competitive with the existing PV/battery technology.     

Experimental investigation on the effect of natural gas composition on performance of autothermal reforming

This paper presents experimental study on catalytic autothermal reforming (ATR) of natural gas (NG) for hydrogen (_H2${\mathrm{H}}_2$) production over sulfide nickel catalyst supported on gamma alumina. The experiments are conducted on a cylindrical reactor of 30 mm in diameter and 200 mm in length with “simulated” NG of different composition under thermal-neutral conditions and fed with different molar air to fuel ratio (A/F$A/F$) and molar water to fuel ratio (W/F)$(W/F)$. The results showed that reforming performance is significantly dependent on A/F$A/F$, W/F$W/F$ and concentration of _C2+${\mathrm{C}}_{2+}$ hydrocarbons in inlet fuel. Fuels containing higher _C2+${\mathrm{C}}_{2+}$ hydrocarbons concentration have optimum performance in terms of more _H2${\mathrm{H}}_2$ at higher A/F$A/F$ and W/F$W/F$ but lower conversion efficiency. Good performance for ATR of fuel containing 15%–20% _C2H6${\mathrm{C}}_2{\mathrm{H}}_6$ can be achieved at A/F=5–7$A/F=5–7$ and W/F=4–6$W/F=4–6$, much higher than that for optimum performance of ATR of methane (A/F=3,W/F=2–2.5$A/F=3,W/F=2–2.5$). _CO2${\mathrm{CO}}_2$ in the inlet fuel does not have significant effect on the reversed water–gas shift reaction. Its effect on reforming performance is mainly due to the dilution of inlet fuel and products.     

Hydrogen storage and induced properties in non-metallic catalytic materials

Particular active sites, ^xM${}^x\mathrm{M}$–^yM^′${}^y{\mathrm{M}}^{\prime }$ (where x$x$ and y$y$ are the number of unsaturations, i.e. anionic vacancies, on each cation M and M^′${\mathrm{M}}^{\prime }$) involving reactive hydrogen are created during the activation of non-metallic catalytic materials. The anionic vacancies created in bulk and at the surface of the solid, by the loss of _H2O${\mathrm{H}}_2\mathrm{O}$ or _H2S${\mathrm{H}}_2\mathrm{S}$, are able to receive hydrogen in a hydridic form according to a heterolytic dissociation (X^2-Mⁿ⁺□+_H2→XH^-Mⁿ⁺H^-${\mathrm{X}}^{2-}{\mathrm{M}}^{n+}\square +{\mathrm{H}}_2\to {\mathrm{XH}}^{-}{\mathrm{M}}^{n+}{\mathrm{H}}^{-}$ with X=O$\mathrm{X}=\mathrm{O}$ or S). The non-metallic catalytic materials become catalytic hydrogen reservoirs. Besides a high reactivity, the hydrogen species, stored in the solid, present marked diffusion properties leading to a dynamic behavior of the solid and active sites.     

CO2 reforming of CH4 by combination of thermal plasma and catalyst

Experiments on synthesis gas preparation from dry reforming of methane by carbon dioxide with thermal plasma only and cooperation of thermal plasma with commercial catalysts have been performed. In all experiments, nitrogen gas was used as the plasma gas to form a high-temperature jet injected into a tube reactor. A mixture of _CH4${\mathrm{CH}}_4$ and _CO2${\mathrm{CO}}_2$ was fed vertically into the jet. Both kinds of experiments were conducted in the same conditions, such as total flux of feed gases, the molar ratio of _CH4/_CO2${\mathrm{CH}}_4/{\mathrm{CO}}_2$, and the plasma power except with or without catalysts in the tube reactor. Higher conversion of _CH4${\mathrm{CH}}_4$ and _CO2${\mathrm{CO}}_2$, higher selectivity of _H2${\mathrm{H}}_2$ and CO, and higher specific energy of the process were achieved by thermal plasma with catalysts. For example, the conversions of _CH4${\mathrm{CH}}_4$ and _CO2${\mathrm{CO}}_2$ were high to 96.33% and 84.63%, and the selectivies of CO and _H2${\mathrm{H}}_2$ were also high to 91.99% and 74.23%, respectively. Both were 10–20%$10–20\%$ higher than those by thermal plasma only.     

Kinetic study on nonisothermal dehydrogenation of TiH2 powders

The nonisothermal dehydrogenation of TiH₂ powders was studied using thermogravimetry and differential scanning calorimetry. The reaction model was established by estimating the activation energy. The results show the nonisothermal dehydrogenation occurred in a four-step process. The hydrogen released from the TiH_1.5∼2$\text{Ti}{\mathrm{H}}_{1.5\sim 2}$ phase in the first step, which led to the decrease of activation energy. The second step was derived from the formation of βH${\beta }_H$ in δ$\delta$ phase and the reaction model was Phase boundary reaction. In the third step, the hydrogen started to release from the βH${\beta }_H$ phase, and then the βH→αH${\beta }_{\mathrm{H}}\to {\alpha }_{\mathrm{H}}$ phase transformation happened. So the activation energy Eα$E_{\alpha }$ underwent a decrease followed by a quick increase. The fourth step corresponded to the formation of αH${\alpha }_H$ in βH${\beta }_H$ phase, and the slight oxidation resulted in the small fluctuation of activation energy.     

Evaluation of conversion efficiency of light to hydrogen energy by Anabaena variabilis

Cyanobacteria provide an efficient system for producing _H2${\mathrm{H}}_2$ from water using solar energy. The energy conversion efficiency can be defined by the ratio of _H2${\mathrm{H}}_2$ produced to the light energy absorbed. An IR and opalescent plate method was used to measure the light energy absorbed. Since cyanobacteria absorb light in the visible range but not in the infrared range, the net amount of light energy absorbed by the cells can be estimated by measuring the IR and visible light intensities transmitted through the biochamber. A rectangular biochamber was used for measuring the conversion efficiency from light energy to _H2${\mathrm{H}}_2$ energy. A quantum meter and radiometer were used to measure the light intensity transmitted through the chamber. Anabaena variabilis was cultured in a BG11 medium with 3.6 mM NaNO₃${}_3$ and the light intensity was 40–50 μmol/m²/s$\mathrm{\mu }\mathrm{mol}/{\mathrm{m}}^2/\mathrm{s}$ in the growth phase and 120–140 μmol/m²/s$\mathrm{\mu }\mathrm{mol}/{\mathrm{m}}^2/\mathrm{s}$ in the _H2${\mathrm{H}}_2$ production phase. The maximum _H2${\mathrm{H}}_2$ production was 50 ml for 40 h and cell density was 1.2 g/l. The _H2${\mathrm{H}}_2$ production rate was 4.1 ml _H2/g${\mathrm{H}}_2/\mathrm{g}$ dry cell weight/h. Based on the light absorbed in the _H2${\mathrm{H}}_2$ production phase, the energy conversion efficiency from light to _H2${\mathrm{H}}_2$ was 1.5% on average and 3.9% at the maximum. Based on the light energy absorbed in the cell growth and _H2${\mathrm{H}}_2$ production phases, the energy conversion efficiency was 1.1% on average.     

Kinetic characteristics of sodium borohydride formation when sodium meta-borate reacts with magnesium and hydrogen

Sodium borohydride is attracting considerable interests as a hydrogen storage medium. In this paper, we investigated the effects of hydrogen pressure, reaction temperature and transition metal addition on sodium borohydride synthesis by the reaction of sodium meta-borate with Mg and _H2${\mathrm{H}}_2$. It was found that higher _H2${\mathrm{H}}_2$ pressure was beneficial to _NaBH4${\mathrm{NaBH}}_4$ formation. The increase in reaction temperature first improved _NaBH4${\mathrm{NaBH}}_4$ formation kinetics but then impeded it when the temperature was raised to near the melting point of Mg. It was also found that some additions of transition metals such as Ni, Fe and Co in the _NaBO2+Mg+_H2${\mathrm{NaBO}}_2+\mathrm{Mg}+{\mathrm{H}}_2$ system promoted the _NaBH4${\mathrm{NaBH}}_4$ formation, but Cu addition showed little effect. The activation energy of the _NaBH4${\mathrm{NaBH}}_4$ formation from Mg, _NaBO2${\mathrm{NaBO}}_2$ and _H2${\mathrm{H}}_2$ was estimated to be 156.3 kJ/mol _NaBH4${\mathrm{NaBH}}_4$ according to Ozawa analysis method.     

H2 production with ultra-low CO selectivity via photocatalytic reforming of methanol on Au/TiO2 catalyst

_H2${\mathrm{H}}_2$ with ultra-low CO concentration was produced via photocatalytic reforming of methanol on Au/_TiO2$\mathrm{Au}/{\mathrm{TiO}}_2$ catalyst. The rate of _H2${\mathrm{H}}_2$ production is greatly increased when the gold particle size is reduced from 10 to smaller than 3 nm. The concentration of CO in _H2${\mathrm{H}}_2$ decreases with reducing the gold particle size of the catalyst. It is suggested that the by-product CO is mostly produced via decomposition of the intermediate formic acid species derived from methanol. The smaller gold particles possibly switch the HCOOH decomposition reaction mainly to _H2${\mathrm{H}}_2$ and _CO2${\mathrm{CO}}_2$ products while suppress the CO and _H2${\mathrm{H}}_2$O products. In addition, some CO may be oxidized to _CO2${\mathrm{CO}}_2$ by photogenerated oxidizing species at the perimeter interface between the small gold particles and _TiO2${\mathrm{TiO}}_2$ under photocatalytic condition.     

Demonstration of sustained hydrogen photoproduction by immobilized,sulfur-deprived Chlamydomonas reinhardtii cells

It was demonstrated that immobilized, sulfur-deprived algal cultures can photoproduce H₂${}_2$. After identifying the optimal material and procedures for immobilization of Chlamyodomonas reinhardtii   at high cell density, we examined the effect of liquid mixing, sulfate content, acetate levels and light intensity on the H₂${}_2$-production activity of the culture. Our results indicate that (a) liquid mixing is important to provide homogeneous conditions for the immobilized culture; (b) sulfur deprivation is necessary for hydrogen production by immobilized cultures; and (c) high light intensity decreases H₂${}_2$ production. The maximum total volume of H₂${}_2$ produced by the system (160 ml of reactor volume) was 380 ml over 23 days, and the highest rate of H₂${}_2$ production observed was 45 ml day^-1${}^{-1}$. Cell immobilization significantly increased the duration of the H₂${}_2$-photoproduction phase (up to 4 weeks), maintained specific rates of H₂${}_2$ photoproduction similar to those of suspension cultures and showed potential for large increases in H₂${}_2$ production.     

Effect of the equivalence ratio,Damköhler number,Lewis number and heat release on the stability of laminar premixed flames in microchannels

The effect of the equivalence ratio on the stability and dynamics of a premixed flame in a planar micro-channel with a step-wise wall temperature profile is numerically investigated using the thermo-diffusive approximation. To characterize the stability behavior of the flame, we construct the stability maps delineating the regions with different flame dynamics in the inlet mass flow rate m   vs. the equivalence ratio ?$?$ parametric space. The flame stability is analyzed for fuels with different diffusivity by changing the Lewis numbers in the range 0.3?_LeF?1.4$0.3?{\mathit{Le}}_F?1.4$. On the other hand, the Lewis number of the oxidizer is kept constant and equal to unity _LeO=1${\mathit{Le}}_O=1$. Our results show that, for very diffusive fuels, the stability of the flame varies significantly with the equivalence ratio, transitioning from stable flames for lean mixtures to highly unstable flames when ?>1$?>1$. As the fuel Lewis number approaches unity, the stability behavior of the flame for lean and rich mixtures becomes more similar to give, in the equidiffusional case _LeF=1${\mathit{Le}}_F=1$, a symmetric stability map around the stoichiometric mixture ?=1$?=1$. In all cases considered, the most stable flames are always found around the stoichiometric mixtures ?=1$?=1$, when the flame instabilities are completely suppressed for very diffusive fuels _LeF<1${\mathit{Le}}_F<1$, or are reduced to a narrow range of inflow velocities for fuel Lewis numbers equal or greater than unity.     

Microstructures and electrochemical characteristics of the La0.75Mg0.25Ni2.5Mx (M=Ni, Co; x=0–1.0) hydrogen storage alloys

In order to investigate the influences of the stoichiometric ratios of B/A (A: gross A-site elements, B: gross B-site elements) and the substitution of Co for Ni on the structure and the electrochemical performances of the _AB2.5–3.5${\mathrm{AB}}_{2.5–3.5}$-type electrode alloys, the La–Mg–Ni–Co system _{La0.75Mg0.25Ni2.5Mx}${\mathrm{La}}_{0.75}{\mathrm{Mg}}_{0.25}{\mathrm{Ni}}_{2.5}{\mathrm{M}}_x$ (M=Ni$\mathrm{M}=\mathrm{Ni}$, Co; x=0$x=0$, 0.2, 0.4, 0.6, 0.8, 1.0) alloys were prepared by induction melting in a helium atmosphere. The structures and electrochemical performances of the alloys were systemically measured. The obtained results show that the structures and electrochemical performances of the alloys are closely relevant to the M content. All the alloys exhibit a multiphase structure, including _LaNi2${\mathrm{LaNi}}_2$, (La,Mg)_Ni3$(\mathrm{La},\mathrm{Mg}){\mathrm{Ni}}_3$ and _LaNi5${\mathrm{LaNi}}_5$ phases, and the major phase in the alloys changes from _LaNi2${\mathrm{LaNi}}_2$ to (La,Mg)_Ni3+_LaNi5$(\mathrm{La},\mathrm{Mg}){\mathrm{Ni}}_3+{\mathrm{LaNi}}_5$ with the variety of M content. The electrochemical performances of the alloys, involving the discharge capacity, the high rate discharge (HRD) ability, the activation capability and the discharge potential characteristics, significantly improve with increasing M content. When M content x$x$ increases from 0 to 1.0, the discharge capacity rises from 177.7 to 343.62  mAh/g for the alloy (M=Ni)$(\mathrm{M}=\mathrm{Ni})$, and from 177.7 to 388.7 mAh/g for the alloy (M=Co)$(\mathrm{M}=\mathrm{Co})$. The cycle stability of the alloy first mounts up then declines with growing M content. The substitution of Co for Ni significantly ameliorates the electrochemical performances. For a fixed M content (x=1.0)$(x=1.0)$, the substitution of Co for Ni enhances the discharge capacity from 343.62 to 388.7 mAh/g, and the capacity retention ratio (_S100)$(S_{100})$ after 100 charging–discharging cycles from 51.45% to 61.1%.     

Hydrogen production from Chlamydomonas reinhardtii biomass using a two-step conversion process: Anaerobic conversion and photosynthetic fermentation

Chlamydomonas reinhardtii UTEX 90 accumulated 1.45 g dry cell weight and 0.77 g starch/L during photosynthetic growth using TAP media at 25 ^°C${}^{°}\mathrm{C}$ in presence of 2% _CO2${\mathrm{CO}}_2$ for 3 days. C. reinhardtii biomass was concentrated and then converted into hydrogen and organic acids by anaerobic fermentation with Clostridium butyricum. Organic acids in the fermentate of algal biomass were consecutively photo-dissimilated to hydrogen by Rhodobacter sphaeroides KD131. In the concentrated algal biomass 52% of the starch was hydrolyzed to 37.1 mmol _H2${\mathrm{H}}_2$/L-concentrated algal biomass and 13.6, 25.5, 7.4 and 493 mM of formate, acetate, propionate, and butyrate, respectively by C. butyricum. R. sphaeroides KD131 evolved 5.72 mmol _H2${\mathrm{H}}_2$ per ml-fermentate of algal biomass under illumination of 8 klux at 30 ^°C${}^{°}\mathrm{C}$. Only 80% of the organic acids, mainly butyrate, were hydrolyzed during photo-incubation. During anaerobic conversion, 2.58 mol _H2/mol${\mathrm{H}}_2/\mathrm{mol}$ starch–glucose was evolved using C. butyricum and then 5.72 mol _H2/L${\mathrm{H}}_2/\mathrm{L}$-anaerobic fermentate was produced by R. sphaeroides KD131. Thus, the two-step conversion process produced 8.30 mol _H2${\mathrm{H}}_2$ from 1 mol starch–glucose equivalent algal biomass via organic acids.