Currently, most of the industrial hydrogen production is based on steam methane reforming process that releases significant amount of CO2 into the atmosphere. CO2 sequestration is one approach to solving the CO2 emission problem for large centralized hydrogen plants, but it would be impractical for decentralized H2 production units. The objective of this paper is to explore new routes to hydrogen production from natural gas without (or drastically reduced) CO2 emissions. One approach analyzed in this paper is based on thermocatalytic decomposition (TCD) of hydrocarbons (e.g., methane) to hydrogen gas and elemental carbon. The paper discusses some technological aspects of the TCD process development: (1) thermodynamic analysis of TCD using AspenPlus TM chemical process simulator, (2) heat input options to the endothermic process, (3) catalyst activity issues, etc. Production of hydrogen and carbon via TCD of methane was experimentally verified using carbon-based catalysts.
Mo rich Mo2C synthesized via a facile two-step synthetic method is potentially a highly active non-noble metal electrocatalyst for hydrogen production via water electrolysis.
A facile and reproducible method for the synthesis of Ag3PO4/TiO2 visible light photocatalyst has been developed to improve the photocatalytic activity and stability of Ag3PO4. The innovation of this method is to in situ deposit Ag3PO4 nanoparticles onto the TiO2 (P25) surface forming a heterostructure. The improved activity of the Ag3PO4/TiO2 heterostructured photocatalyst for the degradation of methylene blue (MB) and rhodamine B (RhB) under visible light irradiation is attributed to the increased surface area and enhanced absorption of MB and RhB. Furthermore, depositing Ag3PO4 onto the surface of TiO2 facilitates electron–hole separation that leads to the elevated photocatalytic activity. The heterostructured Ag3PO4/TiO2 photocatalyst significantly decreases the loading of noble metal Ag from 77 wt% to 47 wt%, thereby significantly reducing the cost for the practical application of Ag3PO4 photocatalyst.
Exposure of specific crystallographic planes as catalyst surfaces has been reported to effectively affect the performance of noble metal cocatalysts used for photocatalytic hydrogen production via water splitting. However, the performance of noble metals for hydrogen production in alkaline solutions is usually 2 orders of magnitude lower than that in acidic media because of the weak dissociative adsorption ability of noble metals to water molecules, which may greatly limit their applications in photocatalytic hydrogen production. In this research we report a Pt-based composite cocatalyst (Ni(OH)2/PtNi nanocubes), designed by separating the dissociative sites of water molecules from active sites for photocatalytic hydrogen production. Compared with PtNi nanocube-loaded CdS, Ni(OH)2/PtNi nanocube-modified CdS exhibits a much higher photocatalytic performance for hydrogen production in alkaline solutions. This study provides a method for synthesizing highly active water-splitting/reducing photocatalysts under alkaline conditions.
Earth-abundant nickel is a typical non-noble-metal cocatalyst used for photocatalytic hydrogen evolution (PHE). Ni nanoparticles, however, tend to aggregate during the hydrogen production process, significantly lowering their PHE activity. To avoid aggregation, we used single atom form Ni and anchored them on vacancies in nitrogen-doped graphene (Ni-NG) as a cocatalyst for PHE. We demonstrated that Ni-NG is a robust and highly active cocatalyst for PHE from water. With only 0.0013 wt % of Ni loading, the PHE activity of composite Ni-NG/CdS photocatalyst improves by 3.4 times compared to that of NG/CdS, and it does not decay even after 10 rounds of 5-hour running. The quantum efficiency of Ni-NG/CdS for PHE reaches 48.2% at 420 nm, one of the highest efficiencies for non-noble-metal-based cocatalysts reported in the literature. Photoluminescence spectral analyses and electrochemical examinations indicated that Ni-NG coupled to CdS serves not only as an electron storage medium to suppress electron–hole recombination but also as an active catalyst for proton reduction reaction. Density functional theory calculations show that the high activity of Ni-NG/CdS composite results from the single Ni atoms trapped in NG vacancies, which significantly reduces the activation energy barrier of the hydrogen evolution reaction. This research may be valuable for developing robust and highly active noble metal free cocatalysts for solar hydrogen production.
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