Nanocomposite for Photocatalytic Hydrogen Production and Method for its Preparation

Methods and systems for reproducible technology for the synthesis of a non platinum based palladium-chromium oxide (Pd-Cr203) loaded cadmium sulfide (CdS) photocatalyst (Pd-Cr203/CdS) for solar photocatalytic hydrogen production via an aqueous ammonium sulfite ((NH4)2SO3) solution. This process is one of the important steps in solar driven photo/thermochemical water splitting cycles. The catalyst preparation follows two steps: Firstly, palladium chloride (PdC12) was used as a precursor that was reduced with sodium borohydride (NaBH4) for the preparation of nanosized palladium metal colloid. Secondly, 0.5g of CdS semiconductor powder was 10 added into the Pd colloid to immobilize Pd-Cr203 nanoparticles onto the surface of CdS forming co-catalyst loaded CdS photocatalyst. Results show that the activity of PdICdS is significantly enhanced by Pd and Cr203 nanocomposites loaded Pd-Cr203/CdS photocatalyst

Solar metal sulfate-ammonia based thermochemical water splitting cycle for hydrogen production.

Two classes of hybrid/thermochemical water splitting processes for the production of hydrogen and oxygen have been proposed based on (1) metal sulfate - ammonia cycles (2)metal pyrosulfate - ammonia cycles. Methods and systems for a metal sulfate MS04 - NH3 cycle for producing H2 and 0 2 from a closed system including feeding an aqueous (NH3)4SO3 solution into a photocatalytic reactor to oxidize the aqueous (NH3)4SO3 into aqueous(NH3)2S04 and reduce water to hydrogen, mixing the resulting aqueous (NH3)2S04 with metal oxide (e.g. ZnO) to form a slurry, heating the slurry of aqueous (NH4)2S04 and ZnO(s)in the low temperature reactor to produce a gaseous mixture of NHs and H20 and solid 10 ZnS04(s), heating solid ZnS04 at a high temperature reactor to produce a gaseous mixture of SO2 and 0 2 and solid product ZnO, mixing the gaseous mixture of SO2 and 02 with an NH3 and H20 stream in an absorber to form aqueous (NH4)2SO3 solution and separate O2 for aqueous solution, recycling the result

Solar Metal Sulfate-Ammonia Based Thermochemical Water Splitting Cycle for Hydrogen Production

Two classes of hybrid/thermochemical water splitting processes for the production of hydrogen and oxygen have been proposed based on (1) metal sulfate-ammonia cycles (2) metal pyrosulfate-ammonia cycles. Methods and systems for a metal sulfate MSO.sub.4--NH3 cycle for producing H2 and O2 from a closed system including feeding an aqueous (NH3)(4)SO3 solution into a photoctalytic reactor to oxidize the aqueous (NH3)(4)SO3 into aqueous (NH3)(2)SO4 and reduce water to hydrogen, mixing the resulting aqueous (NH3)(2)SO4 with metal oxide (e.g. ZnO) to form a slurry, heating the slurry of aqueous (NH4)(2)SO4 and ZnO(s) in the low temperature reactor to produce a gaseous mixture of NH3 and H2O and solid ZnSO4(s), heating solid ZnSO4 at a high temperature reactor to produce a gaseous mixture of SO2 and O2 and solid product ZnO, mixing the gaseous mixture of SO2 and O2 with an NH3 and H2O stream in an absorber to form aqueous (NH4)(2)SO3 solution and separate O2 for aqueous solution, recycling the resultant solution back to the photoreactor and sending ZnO to mix with aqueous (NH4)(2)SO4 solution to close the water splitting cycle wherein gaseous H2 and O2 are the only products output from the closed ZnSO4--NH3 cycle

Method and System for Hydrogen Sulfide Removal

Electrochemical redox methods and systems for implementing for continuous removal of hydrogen sulfide and other sulfur species from sour gas mixtures using transitional metal oxide, sulfide, or carbonate compounds which are regenerated. In one embodiment, in the overall reaction hydrogen sulfide is converted into hydrogen and sulfur: H2S(g) = H2(g) + S(s); applied ^E = 0.20 ~ 0.50 V The columbic efficiency of both methods generally exceeds 90%

Solar Hydrogen Production Via Pulse Electrolysis Of Aqueous Ammonium Sulfite Solution

A long-standing challenge for hydrogen production via solar water splitting is the efficiency of converting solar energy to hydrogen chemical energy. Thermolysis, photocatalysis and electrolysis are three basic solar water splitting processes that utilize solar thermal, photonic and electrical energies. A technology using a combination of these processes can utilize a wider spectrum of solar radiation, thereby enhancing the efficiency of solar energy conversion. Due to the simplicity and maturity of photovoltaic (PV) cells and electrolyzer cells, solar hydrogen production via PV cells plus water electrolysis has been implemented and widely used as a bench mark process. The present study focuses on solar hydrogen production via direct current pulse electrochemical oxidation of aqueous ammonium sulfite solutions, one important step in solar sulfur-ammonia (S-NH3) thermochemical water splitting cycles. The results show that pulsating electrolysis enhances the efficiency of hydrogen production. The effects of pulsating parameters (such as pulsating on time and off time, frequency and duty cycle) on hydrogen evolution rates are discussed in detail. © 2012 Elsevier Ltd

UV Photochemical Option for Closed Cycle Decomposition of Hydrogen Sulfide

Methods and systems for separating hydrogen and sulfur from hydrogen sulfide(H.sub.2S) gas. Hydrogen sulfide(H.sub.2S) gas is passed into a scrubber and filtration unit with polysulfide solution. Interaction frees elemental sulfur which is filtered, excess continues to a stripper unit where the excess H.sub.2S is removed. The excess H.sub.2S returns to the scrubber and filtration unit, while the sulfide solution passes into a photoreactor containing a photocatalyst and a light source. The sulfide solution is oxidatively converted to elemental sulfur and complexed with excess sulfide ion to make polysulfide ion, while water is reduced to hydrogen. Hydrogen is released, while the polysulfide solution is fed back to the scrubber unit where the system operation repeats. In a second embodiment, the photocatalyst is eliminated, and the hydrogen sulfide solution is directly illuminated with ultraviolet radiation with a light source such as a low pressure mercury lamp operating at approximate

Analyses Of Hydrogen Production From Sub-Quality Natural Gas (Ii): Stem Reforming And Autothermal Stem Reforming Of Sqng

Steam reforming of sub-quality natural gas (SRSQNG) can be a more desirable approach for hydrogen production than direct thermolysis of SQNG because the processes produce two more moles of hydrogen via water splitting. A Gibbs reactor unit operation in the AspenPlus™ chemical process simulator has been employed to carry out equilibrium calculations for the SQNG + H2O and SQNG + H2O + O2 systems. Water and oxygen inlet flow rates do not significantly affect the decomposition of H2S at \u3c 1000°C. The major co-product of the processes is carbonyl sulfide while sulfur dimer and carbon disulfide (CS2) are minor by-products within this temperature range. At \u3e 1300°C), CS2 and sulfur dimer become major co-products. No acid gas components are generated. This is an abstract of a paper presented at the 230th ACS National Meeting (Washington, DC 8/28/2005-9/1/2005)

Energy Saving Water Electrolysis For Solar H 2 Production

There are basically three processes (thermolysis, photocatalysis and electrolysis) that can be used for solar hydrogen production via water splitting. A long standing challenge for solar hydrogen production has been to increase the energy efficiency and reduce the cost. Electricity generated from photovoltaic (PV) cells to electrolyze water for hydrogen production has been implemented and widely used for decades. The advantages of this process are simplicity and maturity of both PV cells and electrolyzer designs and configurations. In this technology there are fundamentally three approaches to increase solar to hydrogen efficiency: (1) increase the conversion efficiency for solar to electrical energy via PV cells; (2) increase the efficiency of water electrolytic cells and (3) reduce the requirement for electrical energy by using high temperature solar thermal energy to reduce the need for Gibbs free energy of water splitting. It is noted that current PV cell efficiency is limited to 10 to 15%. Therefore the efficiency improvement must focus on electrolyzer configurations and, alternatively, on using thermochemical water splitting cycles to reduce the potential requirement for hydrogen production. Proton Exchange Membrane (PEM) based water electrolyzers are more compact and have shown higher efficiency than that of conventional alkaline solution based electrolyzers. Energy efficiency of PEM water electrolyzer depends on many factors such as cell configurations and electro catalysts as well as current collectors. We have found that current conductors in a PEM electrolyzer cell play an important role in the enhancement of cell current density. This paper addresses some approaches to achieving higher solar to hydrogen efficiencies via water splitting, focusing on investigation of effects of current collectors as well as electrolysis using pulsating potential technology. Copyright © (2011) by the American Solar Energy Society

Liquid Hydrogen Production Via Hydrogen Sulfide Methane Reformation

H2S is a common contaminant in many of the world\u27s natural gas wells. A discussion on liquid hydrogen production via H2S methane reformation covers thermodynamics; carbon yields at various temperatures; process flowsheet and efficiency computations; gaseous hydrogen production; and overall energy requirements for hydrogen production

Impurity Mitigation Strategies

Understanding of impurities of hydrogen fuel streams in terms of their sources and properties is the first step in the development of alleviation strategies. Impurities in hydrogen may originate from either hydrogen production feedstock or from production processes. They may also derive from onboard hydrogen storage materials. It is self-evident that if an impurity can be removed at its source there will be no need for a pretreatment process in the fuel system of a vehicle. The impurity can also be eliminated during the pretreatment step. In either case, the requirements for proton exchange membrane (PEM) fuel cell catalysts will be lowered