Theoretical model and experimental analysis of a high pressure PEM water electrolyser for hydrogen production

This work aims at analysing the performances of a prototype of a high pressure Polymer Electrolyte Membrane water electrolyser.     

Simple PEM water electrolyser model and experimental validation

We propose in this work a simple model for atmospheric or low-pressure PEM water electrolysers, which allows for simulating the electrochemical, thermal and H₂ output flow behaviours with enough precision for engineering applications. The model has been validated by good agreement with experimental measurements performed in two different electrolysers. The electrochemical submodel allows for obtaining the operating stack voltage from the input current and the stack temperature conditions. After non-linear fitting and statistical analysis from experimental data we conclude that the electrochemical submodel can be extrapolated for any PEM water electrolyser knowing two parameters with physical meaning: activation energy of the “water oxidation” for the anode electrocatalyst and the activation energy for proton transport in the solid polymer membrane. This submodel was validated with experimental polarisation curves at different temperatures from two different PEM water electrolysers. The standard error of the model was less than 0.03. The results showed that the worst values of the estimation were obtained below 50 °C, indicating that the assumption of constant anode charge transfer coefficient is not true at lower temperature, which is in accordance with recent results. In order to complete the electrochemical submodel, a practical methodology is presented here to obtain simple semi-empirical submodels for the H₂ production and thermal behaviours for this kind of electrolysers. Both submodels are also discussed based on the experimental validations.     

Towards the integration of dark- and photo-fermentative waste treatment. 2. Optimization of starch-dependent fermentative hydrogen production

Eight natural microbial consortia collected from different sites were tested for dark, hydrogen production during starch degradation. The most active consortium was from silo pit liquid under mesophilic (37 °C) conditions. The fermentation medium for this consortium was optimized (Fe, NH₄⁺, phosphates, peptone, and starch content) for both dark fermentation and for subsequent purple photosynthetic bacterial H₂ photoproduction [Laurinavichene TV, Tekucheva DN, Laurinavichius KS, Ghirardi ML, Seibert M, Tsygankov AA. Towards the integration of dark and photo fermentative waste treatment. 1. Hydrogen photoproduction by purple bacterium Rhodobacter capsulatus using potential products of starch fermentation. Int J Hydrogen Energy 2008;33(23):7020–26], in the presence of the spent dark, fermentation effluent. The addition of Zn (10 mg L⁻¹), as a methanogenesis inhibitor that does not inhibit purple bacteria at this concentration, also did not inhibit dark, fermentative H₂ production. The influence of various fermentation end products at different concentrations (up to 30 g L⁻¹) on dark, H₂ production was also examined. Added lactate stimulated, but added isobutyrate and butanol strongly inhibited gas production. Under optimal conditions the fermentation of starch (30 g L⁻¹) resulted in 5.7 L H₂ L⁻¹ of culture (1.6 mol H₂ per mole of hexose) with the co-production mainly of butyrate and acetate.     

Ni/SiO2 core–shell catalysts for catalytic hydrogen production from waste plastics-derived syngas

Ni/SiO₂ core–shell catalysts were prepared by deposition–precipitation method and used to produce hydrogen from waste plastics-derived syngas. The SiO₂ core synthesized by the Stöber process was used as the support. This core was synthesized using various solvents, and the effect of these solvents on the morphologies and catalytic performance of the Ni/SiO₂ core–shell catalysts was investigated. The synthesis parameters of the Ni/SiO₂ catalysts were further investigated to enhance the metal–support interaction and dispersion of Ni on the SiO₂ support. The highest catalytic activity of 181 mmol/g-h was achieved when the Ni/SiO₂ core–shell catalyst was synthesized in methanol (Ni/SiO₂–M) and reacted at 800 °C at a water-addition rate of 0.75 g-H₂O/h. The Ni/SiO₂–M catalyst, which possessed strong metal–support interaction nickel phyllosilicates, high specific area, small particle size, and homogeneous metal dispersion, exhibited the best long-term stability.     

Effects of N/C,P/C and Fe/C ratios on dark fermentative hydrogen gas production from waste paper towel hydrolysate

The effects of N/C, P/C and Fe/C ratios on dark fermentative hydrogen gas production from activated carbon treated WPT hydrolysate were investigated using Box–Behnken statistical experiment design. N/C, P/C and Fe/C ratios were chosen as independent variables while the H₂ yield and SHPR were set as the objective functions. H₂ yield and SHPR functions were described by two quadratic model functions. The addition of a proper amount of N, P and Fe to the fermentation media was found to be essential to enhance the H₂ production performance. Linear and interaction terms of N/C and Fe/C did have a significant effect on the H₂ yield in the model function. However, the SHPR was significantly affected by the linear and interaction terms of N/C and P/C. The most convenient N/C, P/C and Fe/C ratios resulting maximum H₂ yield (0.656 mol H₂/mol glucose) and SHPR (241.64 mL H₂/g biomass.h) were determined as 0.05, 0.09 and 0.003 (w/w), respectively.     

Effects of solid particle aspect ratio on the performance of hydrogen production by electrolyzed water

Hydrogen energy has become one of the important directions of future energy development. The hydrogen produced by electrolyzed water is regarded as "green hydrogen", is clean and pollution-free, and is considered the ultimate direction of hydrogen production. If the waste heat of solid particles can be used as the energy required for the water electrolysis process, the cost of "green hydrogen" will be much lower than that of fossil fuel hydrogen production. In order to study the effect of particle structure size on hydrogen production capacity, the heat transfer model of the ellipsoidal particles packed bed with single-vacancy was constructed. Further, the temperature, the apparent thermal resistance, the average heat flux, and the vacancy affects area were studied. With the increase of the particle aspect ratio, the apparent thermal resistance decreases, the average heat flux increase, and hydrogen production increases. When the particle aspect ratio increases from 0.5 to 2.0, the average heat flux of the packed bed with single-vacancy increases from 23.13 kW/m² to 28.87 kW/m², and the apparent thermal resistance decreases from 23.33 K/W to 9.27 K/W. As the particle aspect ratio increases, the area affected by single-vacancy increases, the hindering effect of the vacancy on the heat flow increases.     

Modelling of hydrogen production in batch cultures of the photosynthetic bacterium Rhodobacter capsulatus

The photosynthetic bacterium, Rhodobacter capsulatus, produces hydrogen under nitrogen-limited, anaerobic, photosynthetic culture conditions, using various carbon substrates. In the present study, the relationship between light intensity and hydrogen production has been modelled in order to predict both the rate of hydrogen production and the amount of hydrogen produced at a given time during batch cultures of R. capsulatus. The experimental data were obtained by investigating the effect of different light intensities (6000–50,000 lux) on hydrogen-producing cultures of R. capsulatus grown in a batch photobioreactor, using lactate as carbon and hydrogen source. The rate of hydrogen production increased with increasing light intensity in a manner that was described by a static Baly model, modified to include the square of the light intensity. In agreement with previous studies, the kinetics of substrate utilization and growth of R. capsulatus was represented by the classical Monod or Michaelis–Menten model. When combined with a dynamic Leudekong–Piret model, the amount of hydrogen produced as a function of time was effectively predicted. These results will be useful for the automatization and control of bioprocesses for the photoproduction of hydrogen.