Photo-electro-chemical chlorination of cuprous chloride with hydrochloric acid for hydrogen production

In this paper, a new photochemical cell is developed and analyzed for copper disproportionation within the Cu–Cl water splitting cycle. In the disproportionation step, cuprous chloride reacts with hydrochloric acid to generate cupric chloride and hydrogen gas. In past literature, it has been demonstrated that this reaction can be conducted electrochemically at 24 bars and 100 °C. This reaction is attractive because it generates compressed hydrogen. Consequently, the work required to compress hydrogen from standard pressure – to 350 bars for example – reduces approximately by 95%. To conduct this reaction electrochemically, the process requires electricity input. Rather than using an external supply, the method proposed in this paper drives the reaction 2CuCl(aq) + 2HCl(aq) → 2CuCl₂(aq) + H₂(g) with photonic energy derived from solar radiation. The photochemical cell comprises one photochemical and one electrochemical reactor separated by a proton conducting membrane. The electrochemical reactor is a half electrolysis cell where CuCl liquid is disproportionated with hydrochloric acid by releasing protons, according to 2CuCl(aq) + 2HCl(g) → 2CuCl₂(aq) + 2H⁺ + 2e⁻. The electrons are transferred to the second reactor by an electron-conducting media, consisting of electrodes and an external circuit. In the photochemical reactor, there are supramolecular complexes dissolved in dimethylformamide that generate multi-electrons at active sites under the influence of solar radiation and catalyze water reduction according to 2H₂O + 2e⁻ → H₂(g) + 2OH⁻. Gaseous hydrogen is collected from above the second reactor, while hydroxyl ions combine with the protons that cross the PEM to supply water according to 2OH⁻ + 2H⁺ → 2H₂O. The overall process is assisted electrically by a dye sensitized solar cell. An optical system including solar concentration, spectral splitting and an optical fibre is developed for enhanced solar energy absorption to supply thermally and electrically the Cu–Cl cycle with energy input. This paper examines the feasibility and expected efficiency of the photochemical disproportionation cell and describes the potential benefits of the thermo-photochemical water splitting process, in contrast to conventional thermochemical water splitting.     

Potential of renewable hydrogen production for energy supply in Hong Kong

Hong Kong is highly vulnerable to energy and economic security due to the heavy dependence on imported fossil fuels. The combustion of fossil fuels also causes serious environmental pollution. Therefore, it is important to explore the opportunities for clean renewable energy for long-term energy supply. Hong Kong has the potential to develop clean renewable hydrogen energy to improve the environmental performance. This paper reviews the recent development of hydrogen production technologies, followed by an overview of the renewable energy sources and a discussion about potential applications for renewable hydrogen production in Hong Kong. The results show that although renewable energy resources cannot entirely satisfy the energy demand in Hong Kong, solar energy, wind power, and biomass are available renewable sources for significant hydrogen production. A system consisting of wind turbines and photovoltaic (PV) panels coupled with electrolyzers is a promising design to produce hydrogen. Biomass, especially organic waste, offers an economical, environmental-friendly way for renewable hydrogen production. The achievable hydrogen energy output would be as much as 40% of the total energy consumption in transportation.     

Efficiency of hydrogen production systems using alternative nuclear energy technologies

Nuclear energy can be used as the primary energy source in centralized hydrogen production through high-temperature thermochemical processes, water electrolysis, or high-temperature steam electrolysis. Energy efficiency is important in providing hydrogen economically and in a climate friendly manner. High operating temperatures are needed for more efficient thermochemical and electrochemical hydrogen production using nuclear energy. Therefore, high-temperature reactors, such as the gas-cooled, molten-salt-cooled and liquid-metal-cooled reactor technologies, are the candidates for use in hydrogen production. Several candidate technologies that span the range from well developed to conceptual are compared in our analysis. Among these alternatives, high-temperature steam electrolysis (HTSE) coupled to an advanced gas reactor cooled by supercritical CO₂ (S-CO₂) and equipped with a supercritical CO₂ power conversion cycle has the potential to provide higher energy efficiency at a lower temperature range than the other alternatives.     

Enhanced photocatalytic hydrogen production over In-rich (Ag–In–Zn)S particles

The ratio of ZnS to AgInS₂ is usually adjusted to tune the band gaps of this quaternary (Ag–In–Zn)S semiconductor to increase photocatalytic activity. In this study, the [Zn]/[Ag] ratio was kept constant. The hydrogen production rate was enhanced by increasing the content of indium sulfide. Compared to the steady H₂ evolution rate obtained with equal moles of indium and silver ([In]/[Ag] = 1, 0.64 L/m² h), that obtained with In-rich photocatalyst ([In]/[Ag] = 2, 3.75 L/m² h) is over 5.86 times higher. The number of nanostep structures, on which the Pt cocatalysts were loaded by photodeposition, increased with the content of indium. The indium-rich samples did not induce phase separation between Ag_xIn_xZn_yS_2x+y and AgIn₅S₈, instead forming a single-phase solid solution. Although the photocatalytic activity decreased slightly for bare In-rich photocatalysts, Pt loading played a critical role in the hydrogen production rate. This study demonstrates the significant effect of In₂S₃ on this unique (Ag–In–Zn)S photocatalyst.     

Comparison of thermochemical,electrolytic, photoelectrolytic and photochemical solar-to-hydrogen production technologies

Hydrogen produced from solar energy is one of the most promising solar energy technologies that can significantly contribute to a sustainable energy supply in the future. This paper discusses the unique advantages of using solar energy over other forms of energy to produce hydrogen. Then it examines the latest research and development progress of various solar-to-hydrogen production technologies based on thermal, electrical, and photon energy. Comparisons are made to include water splitting methods, solar energy forms, energy efficiency, basic components needed by the processes, and engineering systems, among others. The definitions of overall solar-to-hydrogen production efficiencies and the categorization criteria for various methods are examined and discussed. The examined methods include thermochemical water splitting, water electrolysis, photoelectrochemical, and photochemical methods, among others. It is concluded that large production scales are more suitable for thermochemical cycles in order to minimize the energy losses caused by high temperature requirements or multiple chemical reactions and auxiliary processes. Water electrolysis powered by solar generated electricity is currently more mature than other technologies. The solar-to-electricity conversion efficiency is the main limitation in the improvement of the overall hydrogen production efficiency. By comparison, solar powered electrolysis, photoelectrochemical and photochemical technologies can be more advantageous for hydrogen fueling stations because fewer processes are needed, external power sources can be avoided, and extra hydrogen distribution systems can be avoided as well. The narrow wavelength ranges of photosensitive materials limit the efficiencies of solar photovoltaic panels, photoelectrodes, and photocatalysts, hence limit the solar-to-hydrogen efficiencies of solar based water electrolysis, photoelectrochemical and photochemical technologies. Extension of the working wavelength of the materials is an important future research direction to improve the solar-to-hydrogen efficiency.     

Analysis of hydrogen production from combined photovoltaics, wind energy and secondary hydroelectricity supply in Brazil

In this work, the technical and economical feasibility for implementing a hypothetical electrolytic hydrogen production plant, powered by electrical energy generated by alternative renewable power sources, wind and solar, and conventional hydroelectricity, was studied mainly trough the analysis of the wind and solar energy potentials for the northeast of Brazil. The hydrogen produced would be exported to countries which do not presently have significant renewable energy sources, but are willing to introduce those sources in their energy system. Hydrogen production was evaluated to be around 56.26 × 10⁶ m³ H₂/yr at a cost of 10.3 US$/kg.     

Performance evaluation of a photoelectrochemical hydrogen production reactor under concentrated and non-concentrated sunlight conditions

In this paper, we present the experimental performance evaluations of a newly developed photoelectrochemical (PEC) reactor for the production of hydrogen under no-light and concentrated solar radiation conditions. With a newly developed experimental setup, the solar light is concentrated about ten times, and the spectrum is divided using cold mirrors for better sunlight utilization. The photoelectrochemical reactor is examined at different applied potentials and the hydrogen production quantities are measured. Copper oxide, which is used as a light-sensitive material, is electrochemically coated on the cathode metal plate to increase the rate of hydrogen evolution under illumination. The present experiments are conducted to investigate the variation of reactor performance with intensified light conditions and the obtained results are compared with the dark conditions. The results of this study reveal that the hydrogen evolution rate was 41.34 mg/h for concentrated light measurement and 34.73 mg/h for no-light measurements at 2.5 V applied potential. The corresponding photocurrent generated under concentrated light at 2.5 V is found to be 0.63 mA/cm². Under the concentrated sunlight, the hydrogen production rates increase considerably which is led by the positive effect of the photocurrent contribution.     

Decoration of Bi2Se3 nanosheets with a thin Bi2SeO2 layer for visible-light-driven overall water splitting

Exploring and developing novel semiconductor photo-catalysts for visible-light-driven water splitting are of great scientific significance to solve energy and environmental problems. Herein, Bismuth Selenide (Bi₂Se₃) nanosheets decorated with a thin layer of Bi₂SeO₂ to form Bi₂Se₃/Bi₂SeO₂ nanocomposites were successfully prepared using a conventional reflux and heating method. Fabricated Bi₂Se₃/Bi₂SeO₂ heterojunctions were characterized via X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy and X-ray photoelectron spectroscopy. It has revealed that, the thickness of outer Bi₂SeO₂ layer can be tuned upon the annealing temperatures, which strongly influenced the performance of catalyst towards water splitting performances. Annealed at 200 °C, the Bi₂Se₃/Bi₂SeO₂ heterojunction with ～5 nm of Bi₂SeO₂ layer yielded the highest hydrogen production rate of 136 μmol g^?1 h^?1. This enhanced photo-catalytic activity was ascribed to the synergy effect between the Bi₂Se₃/Bi₂SeO₂ layer, increased the visible light absorbance capacity, adjustment of the band gap and accelerate the electron-hole separation efficiency. The results represent a simply solution-based method towards a material with high photo-catalytic performance through the appropriate regulation of the oxidation degree of Bi₂Se₃ nanosheets, promising their industrial applications.     

Hydrogen production by splitting water on solid acid materials by thermal dissociation

Conventionally, there have been three basic ways of research on H₂ production from H₂O-splitting with solar energy: photo-catalytic, photo-electrochemical and thermochemical. Among them the thermal dissociation of H₂O has been considered the most efficient, because it is a single step energy conversion process and gives much higher conversion efficiency than those resulted from other methods. However, the major stumbling block of thermal dissociation of H₂O has been the requirement of a high dissociation temperature which causes problems both with materials for the reactor and with energy conversion efficiency for the process. In this study, we show that the dissociation temperature can be drastically lowered when H₂O is thermally dissociated on solid acid materials. A probable mechanism of the thermal H₂O-splitting on solid acid materials is also presented, based on some experimental results of this study and reports in the literature.     

Oxidation reaction kinetics for the steam-iron process in support of hydrogen production

A hydrogen generation research program is focused on solar-driven hydrogen production by means of reactive metal water splitting. In order to dissociate water molecules at significantly reduced thermal energies as well as providing a practical means for efficient hydrogen and oxygen separation, an intermediary reactive material is introduced to realize water splitting in the form of an oxidation reaction. Elemental iron is used as the reactive material in the process commonly referred to as the steam-iron process. In order to exploit the unique characteristics of highly reactive materials and ultimately achieve the potential efficiency gains at the solar reactor scale, a monolithic laboratory-scale reactor has been designed to explore the fundamental kinetic rates during the iron oxidation reaction at temperatures ranging from about 650 to 900 K. Results show hydrogen production rates on the order of 1E-8 g/cm² s. Micro-Raman spectroscopy is used to access information on the exact iron oxide phase produced, and high resolution SEM and electron dispersion spectroscopy (EDS) are used to assess the oxide morphology and further quantify the oxide state, including spatial distributions.