Vertically oriented graphene (VG) nanosheets have attracted growing interest for a wide range of applications, from energy storage, catalysis and field emission to gas sensing, due to their unique orientation, exposed sharp edges, non-stacking morphology, and huge surface-to-volume ratio. Plasma-enhanced chemical vapor deposition (PECVD) has emerged as a key method for VG synthesis; however, controllable growth of VG with desirable characteristics for specific applications remains a challenge. This paper attempts to summarize the state-of-the-art research on PECVD growth of VG nanosheets to provide guidelines on the design of plasma sources and operation parameters, and to offer a perspective on outstanding challenges that need to be overcome to enable commercial applications of VG. The review starts with an overview of various types of existing PECVD processes for VG growth, and then moves on to research on the influences of feedstock gas, temperature, and pressure on VG growth, substrate pretreatment, the growth of VG patterns on planar substrates, and VG growth on cylindrical and carbon nanotube (CNT) substrates. The review ends with a discussion on challenges and future directions for PECVD growth of VG.

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Plasma-enhanced chemical vapor deposition synthesis of vertically oriented graphene nanosheets

Ammonia as an effective hydrogen carrier and a clean fuel for solid oxide fuel cells

Recent advances in technologies for the decentralized, islanded ammonia economy are reviewed, with an emphasis on feasibility for long-term practical implementation. The emphasis in this review is on storage systems in the size range of 1–10 MW. Alternatives for hydrogen production, nitrogen production, ammonia synthesis, ammonia separation, ammonia storage, and ammonia combustion are compared and evaluated. A conceptual process design, based on the optimization of temperature and pressure levels of existing and recently proposed technologies, is presented for an islanded ammonia energy system. This process design consists of wind turbines and solar panels for electricity generation, a battery for short-term energy storage, an electrolyzer for hydrogen production, a pressure swing adsorption unit for nitrogen production, a novel ruthenium-based catalyst for ammonia synthesis, a supported metal halide for ammonia separation and storage, and an ammonia fueled, proton-conducting solid oxide fuel cell for electricity generation. In a generic location in northern Europe, it is possible to operate the islanded energy system at a round-trip efficiency of 61% and at a cost of about 0.30–0.35 € kWh−1.

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Islanded ammonia power systems: Technology review & conceptual process design

Conventional technologies are largely powered by fossil fuel exploitation and have ultimately led to extensive environmental concerns. Hydrogen is an excellent carbon-free energy carrier, but its storage and long-distance transportation remain big challenges. Ammonia, however, is a promising indirect hydrogen storage medium that has well-established storage and transportation links to make it an accessible fuel source. Moreover, the notion of ‘green ammonia’ synthesised from renewable energy sources is an emerging topic that may open significant markets and provide a pathway to decarbonise a variety of applications reliant on fossil fuels. Herein, a comparative study based on the chosen design, working principles, advantages and disadvantages of direct ammonia fuel cells is summarised. This work aims to review the most recent advances in ammonia fuel cells and demonstrates how close this technology type is to integration with future applications. At present, several challenges such as material selection, NOx formation, CO2 tolerance, limited power densities and long term stability must still be overcome and are also addressed within the contents of this review.

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Recent progress in ammonia fuel cells and their potential applications

The carbon dioxide concentrator by using MCFC

Platinum catalysts supported on carbon nanowalls (Pt/CNW) were prepared by a solution-reduction method. It is shown that Pt nanoparticles with a mean diameter of 3.5 nm are well dispersed along domain boundaries in each CNW. In addition, it is shown that the Pt/CNW has high electrochemical active surface area and utilization, comparable to those for commercially available T–Pt/CB with good performance. Such high electrocatalytic activity could be attributed to the high electric conductivity of CNW and the improvement of electronic properties of Pt nanoparticles on the domain boundaries, in addition to the high dispersion of Pt particles.

Carbon nanowalls as platinum support for fuel cells

Development of 1 kW-class Ammonia-fueled Solid Oxide Fuel Cell Stack

High Temperature Electrochemical Separation of Carbon Dioxide Using Molten Carbonate

Disclosed is a method for producing perchlorate, which comprises: an electrolysis step (S1) wherein an electrolysis vessel (2), in which a positive electrode side (4A) on which a positive electrode (4) is arranged and a negative electrode side (5A) on which a negative electrode (5) is arranged are divided by a cation-exchange membrane (6), is used and an aqueous solution of sodium chlorate is electrolytically oxidized on the positive electrode side (4A) of the electrolysis vessel (2); a neutralization reaction step (S2) wherein a substance an aqueous solution of which shows alkalinity is added to the aqueous perchloric acid solution that has been produced by the electrolytic oxidation on the positive electrode side, so that perchlorate is synthesized by a neutralization reaction; and a crystallization process wherein the perchlorate synthesized by the neutralization reaction is obtained as crystals. The crystallization process is composed of an evaporative crystallization step (S3), or alternatively composed of three steps, namely an evaporative concentration step (S21), a cooling crystallization step (S22), and a separation step (S23).

Takahiro Matsuo

Papers

Carbon nanowalls as platinum support for fuel cells

Development of 1 kW-class Ammonia-fueled Solid Oxide Fuel Cell Stack

High Temperature Electrochemical Separation of Carbon Dioxide Using Molten Carbonate

Method and apparatus for producing perchlorate

Fe-N-doped carbon catalysts prepared by hybrid PECVD/sputtering system for oxygen reduction reaction