There is still an ongoing effort to search for sustainable, clean and highly efficient energy generation to satisfy the energy needs of modern society. Among various advanced technologies, electrocatalysis for the oxygen evolution reaction (OER) plays a key role and numerous new electrocatalysts have been developed to improve the efficiency of gas evolution. Along the way, enormous effort has been devoted to finding high-performance electrocatalysts, which has also stimulated the invention of new techniques to investigate the properties of materials or the fundamental mechanism of the OER. This accumulated knowledge not only establishes the foundation of the mechanism of the OER, but also points out the important criteria for a good electrocatalyst based on a variety of studies. Even though it may be difficult to include all cases, the aim of this review is to inspect the current progress and offer a comprehensive insight toward the OER. This review begins with examining the theoretical principles of electrode kinetics and some measurement criteria for achieving a fair evaluation among the catalysts. The second part of this review acquaints some materials for performing OER activity, in which the metal oxide materials build the basis of OER mechanism while non-oxide materials exhibit greatly promising performance toward overall water-splitting. Attention of this review is also paid to in situ approaches to electrocatalytic behavior during OER, and this information is crucial and can provide efficient strategies to design perfect electrocatalysts for OER. Finally, the OER mechanism from the perspective of both recent experimental and theoretical investigations is discussed, as well as probable strategies for improving OER performance with regards to future developments.

Electrocatalysis for the oxygen evolution reaction: recent development and future perspectives

Renewable Resources Robert-Jan van Putten,†,‡ Jan C. van der Waal,† Ed de Jong,*,† Carolus B. Rasrendra,‡,⊥ Hero J. Heeres,*,‡ and Johannes G. de Vries* †Avantium Chemicals, Zekeringstraat 29, 1014 BV Amsterdam, the Netherlands ‡Department of Chemical Engineering, University of Groningen, Nijenborgh 4, 9747 AG Groningen, the Netherlands Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, the Netherlands DSM Innovative Synthesis BV, P.O. Box 18, 6160 MD Geleen, the Netherlands Department of Chemical Engineering, Institut Teknologi Bandung, Ganesha 10, Bandung 40132, Indonesia

Hydroxymethylfurfural, A Versatile Platform Chemical Made from Renewable Resources

Although sunlight-driven water splitting is a promising route to sustainable hydrogen fuel production, widespread implementation is hampered by the expense of the necessary photovoltaic and photoelectrochemical apparatus. Here, we describe a highly efficient and low-cost water-splitting cell combining a state-of-the-art solution-processed perovskite tandem solar cell and a bifunctional Earth-abundant catalyst. The catalyst electrode, a NiFe layered double hydroxide, exhibits high activity toward both the oxygen and hydrogen evolution reactions in alkaline electrolyte. The combination of the two yields a water-splitting photocurrent density of around 10 milliamperes per square centimeter, corresponding to a solar-to-hydrogen efficiency of 12.3%. Currently, the perovskite instability limits the cell lifetime.

http://science.sciencemag.org/content/sci/345/6204/1593.full.pdf

Water photolysis at 12.3% efficiency via perovskite photovoltaics and Earth-abundant catalysts

A review on the utilization of fly ash

Water electrolysis is considered as the most promising technology for hydrogen production. Much research has been devoted to developing efficient electrocatalysts for hydrogen production via the hydrogen evolution reaction (HER) and oxygen production via the oxygen evolution reaction (OER). The optimum electrocatalysts can drive down the energy costs needed for water splitting via lowering the overpotential. A number of cobalt (Co)-based materials have been developed over past years as non-noble-metal heterogeneous electrocatalysts for HER and OER. Recent progress in this field is summarized here, especially highlighting several important bifunctional catalysts. Various approaches to improve or optimize the electrocatalysts are introduced. Finally, the current existing challenges and the future working directions for enhancing the performance of Co-implicated electrocatalysts are proposed.

Recent Progress in Cobalt‐Based Heterogeneous Catalysts for Electrochemical Water Splitting

Inorganic matter in coal continues to be one of the major sources of operational problems during coal combustion. The role of inorganic matter during coal combustion is governed by its nature and occurrence in the coal matrix [Raask‚ 1985]. In pulverised coal combustion processes‚ slagging‚ fouling and corrosion are the main problems which arise from the coal mineral matter. These problems can be even more severe when firing low-rank coals with high alkaline and transition metal ions. In contrast‚ fluidised bed combustion processes operating at much lower tempearures ( 800–900 °C) offer better prospects for reducing ash-related problems associated with the firing of low-rank coals. However‚ low-rank coals do not present trouble-free operation in fluidised beds. A major problem is presented by particle agglomeration‚ bed defluidization and ash deposition on heat exchanger surfaces. The inorganic constituents in low-rank coals (mainly sodium‚ calcium and organically bound sulphur) transform to low-melting eutectics at fluid bed operating temperatures [Manzoori and Agarwal‚ 1993; Hodges and Richards‚ 1989; Manzoori and Agarwal‚ 1992; Souto et al.‚ 1996]. These eutectics are transferred to the surface of inert bed particles leading to agglomeration and defluidization of the bed. This phenomenon is dependant to a great extent on the operating temperature of the fluid bed combustor. The present work is aimed at understanding the effects of bed temperature on ash characteristics during fluid bed combustion of an Australian and an Indonesian low-rank coal. Data is presented to demonstrate the effect of bed temperature on the distribution of inorganic matter into variuos streams such as bed ash and cyclone ash. Comparisons of the characteristics of ash deposition on bed material and bed defluidization for Australian and Indonesian low-rank coals are presented. In addition‚ the chemical nature of the ash deposits is discussed‚ along with the chemical interactions that might have occurred during the combustion experiments to cause ash-related problems.

Role of Inorganics During Fluidised-Bed Combustion of Low-Rank Coals

In this study, ZSM-5 zeolites with crystal sizes ranging from 0.1 mum to 30 mum were synthesized, and their catalytic performance in methanol to gasoline (MTG) reactions was evaluated in terms of methanol conversion, product distribution, and coke formation. It was found that decreasing the ZSM-5 crystal size significantly improved methanol conversion and gasoline selectivity, in the meantime, reduced coking on the catalyst. It is believed that reducing crystal size effectively shortened the diffusion path length for the reactant to reach and for the reaction products to escape from the active sites within the micropores of ZSM-5. The shorter diffusion path also facilitated the escape of intermediates formed during methanol reaction, thus reduced the coke formation.

Effect of Crystal Size of ZSM-5 on its Catalytic Activity for Methanol to Gasoline Conversion

An innovative technology to integrate the utilization of biochar and algae in the form of slurry fuel for power generation was conceptualized. This study aimed to understand the rheological properties and stability characteristics of biochar–algae–water (BAW) slurry fuels. The BAW slurries were prepared by mixing pine sawdust biochar and Chlorella vulgaris in different proportions first and then dispersing the mixtures in deionized water. The BAW slurries showed shear-thinning flow behavior, which became more apparent as the algae proportion in the solid increased. The slurries displayed better stability at higher algae proportion due to increased water uptake capacity and enhanced flocculation.

An experimental study of the rheological properties and stability characteristics of biochar–algae–water slurry fuels

Particle size and heat transfer effects on organic and inorganic sulphur transformations during pyrolysis are investigated using temperature-programmed pyrolysis and fixed-bed pyrolysis (700-900°C) of pulverised Bowmans coal, and fluidised bed pyrolysis at 800°C of 6, 8 and 10mm diameter cylindrical coal pellets. Results are interpreted using a heat transfer model [8]. The pyrolysis experiments reveal that during the initial devolatilisation stage, organic and sulphate sulphur decomposition occurs at a rate directly proportional to heating rate and inversely proportional to particle size. Towards the end of the devolatilisation stage, the transportation of volatiles out of the coal decreases so that sulphate undergoes solid-state transformations to form organic sulphur in the char. The reincorporation process is accelerated by higher reaction temperatures or heating rates which allows greater decomposition of sulphate and longer periods of slow devolatilisation to support the solid-state reactions. Smaller particles in the fluidised bed reveal a similar effect due to faster internal heating rates. Larger particle sizes also facilitate organic sulphur increase due to slow internal heating rates and hence slow and extended devolatilisation and sulphate reincorporation.

The Effect of Particle Size and Heating Rate on the Transformation of Sulphur during Pyrolysis of a South Australian Low-rank Coal

A mathematical model has been developed to predict the temperature response of dry low-rank coal particles during pyrolysis in an inert atmosphere. The model is based on the unsteady-state heat conduction equation in spherical coordinates and uses the Distributed Activation Energy Model to predict volatiles evolution. Measurements of the temperature response at the centre of 10mm Bowmans coal particles were conducted in a horizontal tube furnace using nitrogen as the heating medium at furnace temperatures of 150dC, 350dC, 600dC, 700dC, and 800dC. A sensitivity analysis was performed to assess the influence of the heat of pyrolysis and the flux of volatiles leaving the particle on the temperature response. The heat of pyrolysis can influence the predicted temperature response, however the uncertainty surrounding the magnitude and nature of its value remains a problem. The gaseous flux has no significant effect on the model predictions. Measurements of the temperature response of particles with varying moisture contents indicate that the presence of moisture significantly influences the temperature response. The effect of moisture is greater than that of the heat of pyrolysis and further work is required to incorporate moisture into the current model.

Dongke Zhang

Papers

Role of Inorganics During Fluidised-Bed Combustion of Low-Rank Coals

Effect of Crystal Size of ZSM-5 on its Catalytic Activity for Methanol to Gasoline Conversion

An experimental study of the rheological properties and stability characteristics of biochar–algae–water slurry fuels

The Effect of Particle Size and Heating Rate on the Transformation of Sulphur during Pyrolysis of a South Australian Low-rank Coal

Mathematical Modelling of Temperature Response of Low-rank Coal Particles during Pyrolysis