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Platinum–carbon catalysts are widely used in the manufacturing of proton-exchange membrane fuel cells. Increasing Pt/C activity and stability is an urgent task and the optimization of their structure seems to be one of the possible solutions. In the present paper, Pt/C electrocatalysts containing small (2–2.6 nm) nanoparticles (NPs) of a similar size, uniformly distributed over the surface of a carbon support, were obtained by the original method of liquid-phase synthesis. A comparative study of the structural characteristics, catalytic activity in the oxygen electroreduction reaction (ORR), and durability of the synthesized catalysts, as well as their commercial analogs, was carried out. It was shown that the uniformity of the structural and morphological characteristics of Pt/C catalysts makes it possible to reduce the negative effect of the small size of NPs on their stability. As a result, the obtained catalysts were significantly superior to their commercial analogs regarding ORR activity, but not inferior to them in terms of stability.

Efficient electrocatalysts for the oxygen evolution reaction (OER) are highly desirable because of the intrinsically sluggish kinetics of OER. Herein, core–shell structured nanospheres of NiFexSn@NiFe (oxy)hydroxide (denoted as NiFexSn‐A) are prepared as active OER catalysts by a facile electrochemical strategy, which includes electrodeposition of NiFexSn alloy nanospheres on carbon cloth (CC) and following anodization. The alloy core of NiFexSn could promote charge transfer, and the amorphous shell of NiFe (oxy)hydroxide is defect‐rich and nanoporous due to the selective electrochemical etching of Sn in alkaline medium. The optimized catalyst of NiFe0.5Sn‐A displays a remarkable OER performance with a low overpotential of 260 mV to reach the current density of 10 mA cm−2, a small Tafel slope of 50 mV dec−1, a high turnover frequency of 0.194 s−1 at an overpotential of 300 mV, and a robust durability. Further characterizations indicate that the superior OER performance of the core–shell structured NiFe0.5Sn‐A nanospheres might originate from abundant active sites and small charge transfer resistance. This work brings a new perspective to the design and synthesis of core–shell structured nanospheres for electrocatalysis through a facile electrochemical strategy., Through a facile electrochemical strategy including the process of electrodeposition and anodization, core–shell structured NiFeSn@NiFe (oxy)hydroxide nanospheres could be easily prepared with good conductivity, abundant active sites, high electrochemically active surface area, enhanced oxygen vacancy defects, and controllable chemical composition, which demonstrate high activity and long‐term durability for electrocatalytic water oxidation in alkaline condition.

Demands for sustainable production of hydrogen are rapidly increasing because of environmental considerations for fossil fuel consumption and development of fuel cell technologies. Thus, the development of high‐performance and economical catalysts has been extensively investigated. In this study, a nanoporous Mo carbide electrode is prepared using a top‐down electrochemical process and it is applied as an electrocatalyst for the hydrogen evolution reaction (HER). Anodic oxidation of Mo foil followed by heat treatment in a carbon monoxide (CO) atmosphere forms a nanostructured Mo carbide with excellent interconnections, and these structural characteristics lead to high activity and durability when applied to the HER. Additionally, characteristic behavior of Mo is observed; metallic Mo nanosheets form during electrochemical anodization by exfoliation along the (110) planes. These nanosheets are viable for chemical modification, indicating their feasibility in various applications. Moreover, the role of carbon shells is investigated on the surface of the electrocatalysts, whereby it is suggested that carbon shells serve as a mechanical barrier against the oxidative degradation of catalysts that accompanies unavoidable volume expansion.

Hydrogen evolution reaction (HER) is one promising technique to obtain high-purity hydrogen, therefore, exploiting inexpensive and high-efficiency HER electrocatalysts is a matter of cardinal significance under the background of achieving carbon neutrality. In this paper, a hydrothermal method was used to prepare the Cr-NiC2O4/NF (Ni foam) precursor. Then, the NiO-Cr-C/NF self-supporting HER catalyst was obtained by heating the precursor at 400 °C. The catalyst presents a 3D cellular nanospheres structure which was composed of 2D nanosheets. Microstructure characterization shows that Cr and C elements were successfully doped into NiO. The results of electrochemical measurements and density functional theory (DFT) calculations show that under the synergy of Cr and C, the conductivity of NiO was improved, and the Gibbs free energy of H* (∆GH*) value is optimized. As a result, in 1.0 M KOH solution the NiO-Cr-C/NF-3 (Ni:Cr = 7:3) HER catalyst exhibits an overpotential of 69 mV and a Tafel slope of 45 mV/dec when the current density is 10 mA·cm−2. Besides, after 20 h of chronopotentiometry, the catalytic activity is basically unchanged. It is demonstrated that C and Cr co-doping on the lattice of NiO prepared by a simple hydrothermal method and subsequent heat treatment to improve the catalytic activity and stability of the non-precious metal HER catalysts in an alkaline medium is facile and efficient.

In spite of significant achievements in alkaline exchange membrane fuel cells (AEMFCs) in recent years, they are still lagging behind proton exchange membrane fuel cells (PEMFCs) due to performance instability. Among the relevant operational parameters of AEMFC, the researchers have found that poor water management within the cell was the main reason for failure of the system. In the past five years, numerous modeling and experimental works were reported proposing different strategies to improve water management of AEMFC. With proper water management, the achievable power output in AEMFCs is comparable with that of PEMFCs or even more. Efforts have to be continued, but AEMFCs can become a strong competitor in the market place. This review paper discusses the strategies and developments impacting water management of AEMFCs providing knowledge source for upcoming studies.

With the approaching commercialization of PEM fuel cell technology, developing active, inexpensive non-precious metal ORR catalyst materials to replace currently used Pt-based catalysts is a necessary and essential requirement in order to reduce the overall system cost. This review paper highlights the progress made over the past 40 years with a detailed discussion of recent works in the area of non-precious metal electrocatalysts for oxygen reduction reaction, a necessary reaction at the PEM fuel cell cathode. Several important kinds of unsupported or carbon supported non-precious metal electrocatalysts for ORR are reviewed, including non-pyrolyzed and pyrolyzed transition metal nitrogen-containing complexes, conductive polymer-based catalysts, transition metal chalcogenides, metal oxides/carbides/nitrides/ oxynitrides/carbonitrides, and enzymatic compounds. Among these candidates, pyrolyzed transition metal nitrogen-containing complexes supported on carbon materials (M-N x/C) are considered the most promising ORR catalysts because they have demonstrated some ORR activity and stability close to that of commercially available Pt/C catalysts. Although great progress has been achieved in this area of research and development, there are still some challenges in both their ORR activity and stability. Regarding the ORR activity, the actual volumetric activity of the most active non-precious metal catalyst is still well below the DOE 2015 target. Regarding the ORR stability, stability tests are generally run at low current densities or low power levels, and the lifetime is far shorter than targets set by DOE. Therefore, improving both the ORR activity and stability are the major short and long term focuses of non-precious metal catalyst research and development. Based on the results achieved in this area, several future research directions are also proposed and discussed in this paper.

Highly efficient and stable electrocatalyst for hydrogen evolution reaction (HER) is essential for the application of green hydrogen energy. To date, platinum-based materials are the most efficient electrocatalyst. Developing inexpensive electrocatalyst with low Pt loading and high platinum utilization efficiency is one of effective strategies to lower the cost of platinum-based electrocatalyst. In this paper, it was demonstrated that ultrafine and uniform distribution platinum nanoparticles could be synthesized on three-dimensional sulfur-doped graphene materials (Pt/3DSG) via covalent cross-linking between platinum and doped sulfur atoms. The high conductive 3DSG not only facilitates the electron transport but also serves as a template for depositing ultrafine and uniform platinum nanoparticles. The Pt/3DSG with low Pt loading (3.1 wt%) delivers extremely outstanding HER performance, which is superior to the commercial 20 wt% Pt/C catalyst. The turnover frequencies (TOFs) of Pt/3DSG can reach 1.12 s(-1), which is larger than that of 20% Pt/C (0.71 s(-1)). Furthermore, the stability is also superior than that of Pt/C. This work provides a rational design strategy for highly efficient and stable electrocatalysts with low loading and high utilization of precious metal. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

With the increasing energy demand, energy conversion and storage technology has garnered intense attention. As one of the competitive electrochemical energy technologies, the zinc–air battery (ZAB) has been considered to be a promising candidate due to its advantages, including low cost and environmental friendliness. To overcome its technical challenges of low activity and stability of ZAB air electrode electrocatalysts, substantial efforts have been made to develop highly active and stable materials for improving the performance. In this paper, a comprehensive review of one type of the ZAB electrocatalyst, that is, iron group (Fe, Co, Ni)-based oxides, is provided. The discussion will be concentrated on the recent progress and challenges associated with this type of electrocatalyst as well as corresponding perspectives.

This paper provides a comprehensive overview of the current state of development of transition metal macrocyclic (TMM) complex-based electrocatalysts used in oxygen reduction reactions (ORRs) in polymer electrolyte membrane fuel cells (PEMFCs). Up to date performances of carbon material-supported TMM catalysts, including both ORR activity rates and stabilities are, discussed. The effects of different types and natures of metals, macrocyclic ligands, ligand substitutions, catalyst supporting materials, electrode preparation, and various acid/alkaline solutions are thoroughly analyzed and reviewed based on the published literature. The ORR mechanisms facilitated by these TMM catalysts are discussed from both a theoretical and experimental observation point of view. Required improvements in ORR activity, stability and commercial viability in order for TMM complex-based electrocatalysts to be utilized in PEMFCs are identified. Potential research directions to overcome current challenges are also suggested to facilitate future efforts in this area.

This paper describes a simple in-situ process of synthesizing highly dispersed palladium nanoparticles (PdNPs) using aqueous leaf extract of GarciniapedunculataRoxb as bio-reductant and starch (0.3%) as bio-stabilizer. The PdNPs are characterized by techniques like FTIR, TEM, SEM-EDX, XRD and XPS analysis. It is worthnoting thatwhen the synthesis of nanoparticles was carried out in absence of starch, agglomeration of particles has been noticed.The starch-assisted PdNPs showed excellent aqueous-phase catalytic activities for three important reactions: the Suzuki-Miyaura cross-coupling reactions of aryl halides (aryl bromides and iodides) with arylboronic acids; selective oxidations of alcohols to corresponding carbonyl compounds; and reduction of toxic Cr(VI) to nontoxic Cr(III). Our catalyst could be reused up to four cycles without much compromising with its activity. Furthermore, the material also demonstrated excellent antimicrobial and anti-biofilm activities against a novel multidrug resistant clinical bacterial isolate Cronobactersakazakii strain AMD04. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of PdNPswere found to be 0.06 and 0.12 mM respectively.

Technological improvements in polymer electrolyte membrane water electrolysers (PEMWEs) are promoted by their exciting possibilities to operate with renewable power sources. In this paper, a synopsis of the research efforts concerning with the development of electrocatalysts, polymer electrolytes and stack hardware components is presented. The most challenging problem for the development of PEMWEs is the enhancement of oxygen evolution reaction rate. At present, there are no practical alternatives to noble metal-based oxide catalysts such as IrO2 and RuO2. As well as carbon supported Pt nanoparticles are the benchmark cathode catalysts for hydrogen evolution. High noble metal loading on the electrodes and the use of perfluorosulfonic membranes significantly contribute to the cost of these devices. Critical areas include the design of appropriate mixed electrocatalysts and their dispersion on low cost Ti-oxide like supports to increase catalyst utilization. Moreover, the development of alternative membranes with enhanced mechanical properties for high pressure applications, proper conductivity and reduced gas cross-over is strongly required. This latter aspect is also addressed by the development of proper recombination catalysts. The development of anodic mixed non-noble transition metal oxides with spinel or perovskite structure and proper resistance to chemical degradation in the acidic environment and electrochemical corrosion is also an active area of research. Similarly, efforts are also being addressed to Pd and Ru based cathode formulations with cheaper characteristics than Pt. Whereas, concerning with stack hardware, cost reduction may be addressed by replacing Ti-based diffusion media and bipolar plates with appropriate and cost-effective stainless steel materials with enhanced resilience to chemical and electrochemical corrosion. Regarding the combination with renewable power sources, PEM electrolysers can find suitable applications for peak shaving in integrated systems grid connected or in grid independent operating conditions where hydrogen generated through electrolysis is stored and then via fuel cell converted back to electricity when needed or used to refill fuel cell-based cars. Hydrogen is the most promising clean energy carrier to accomplish the sustainable production of energy and a synergy among hydrogen, electricity and renewable energy sources is highly desired.

The physico-chemical and application properties of phenol-formaldehyde resins used in the production of laminated plastics depend on such factors as: type and amount of catalyst, formaldehyde-to-phenol mole ratio, temperature and time of the synthesis process. The special impact on the reaction mechanism and kinetics, e.g. on the formation of mono-, di- and trihydroxymethyl derivatives of phenol (PhOH) is a consequence of the type and amount of the catalyst. This paper presents the results of optimisation research of resol resin synthesis catalysed by trimethylamine (TEA) carried out according to 32 experimental design. The aim of the research was to determine the synthesis conditions under which it is possible to achieve products with reduced content of unconverted formaldehyde (CH2O), phenol and its hydroxymetyl derivatives, while maintaining the required physico-chemical properties. The process employing selected polyamines as well as TEA together with polyamine co-catalysts i.e. diethylenetriamine (DETA) and triethylenetetraamine (TETA) was also studied. The results were compared with those of the resins which were synthesised with the use of classic catalysts-ammonia (NH3) and triethylamine for which the content of CH2O, PhOH and its hydroxymethyl derivatives was respectively: NH3-5.13% and 46.27%, TEA-0.33% and 52.41%. In the case DETA was added, the content of phenol and its hydroxymethyl derivatives could be reduced by 52.49% in relation to the resin obtained with the use of TEA and by 46.19% in relation to the resin obtained with the use of ammonia. The formaldehyde content was reduced by 78.79% and 98.64%, respectively. When TETA was added as a co-catalyst, the content of phenol and its derivatives was reduced by 48.04% versus triethylamine-catalysed resin and by 41.15% versus ammonia-catalysed material. The reduction in formaldehyde content reached 84.85% and 99.03%, respectively. The results of kinetic study were also presented, the prediction accuracy of the proposed kinetic model is more than 98% for all the catalysts in the state variable space. Polyamine co-catalysts gave much higher rate constants (0.50 and 0.45 for TETA and DETA, respectively).

In this paper, carbon supported noble metal nanoparticles synthesized by using Keggin type polyoxometalate (POM), silicotungstic acid (STA), were effectively utilized as electrodes in an effort to improve the efficiency of electrochemical energy conversion processes related to direct methanol fuel cells. The excellent electron transfer and strong adsorption abilities of STA have been well exploited for the reduction of metal ions as well as the modification of carbon support to form Pt and Pt-Ru metal nanoparticles supported on carbon nanostructure composites (Pt/STA-C and Pt-Ru/STA-C) under microwave irradiation. Transmission electron microscopy results indicated that well-dispersed metal nanoparticles were formed on the carbon support. The electrocatalytic properties of Pt/STA-C and Pt-Ru/STA-C were analyzed by cyclic voltammetry and chronoamperometry through the methanol oxidation reaction for fuel cell applications. As compared with the commercial Pt-Ru/C (Johnson Matthey) and Pt/C and Pt-Ru/C electrocatalysts prepared by using the common hydrogen reduction method, the STA containing Pt/STA-C and Pt-Ru/STA-C synthesized by the method developed in this work exhibited lower onset potential, high activity with enhanced stability, and better tolerance toward poisoning by CO for the methanol oxidation reaction. �2009 American Chemical Society.

This paper presents a numerical and experimental study on the performance of a methanol steam reformer integrated with a hydrogen/air combustion reactor for hydrogen production. A CFD-based 3D model with mass and momentum transport and temperature characteristics is established. The simulation results show that better performance is achieved in the cross-U type reactor compared to either a tubular reactor or a parallel-U type reactor because of more effective heat transfer characteristics. Furthermore, Cu-based micro reformers of both cross-U and parallel-U type reactors are designed, fabricated and tested for experimental validation. Under the same condition for reforming and combustion, the results demonstrate that higher methanol conversion is achievable in cross-U type reactor. However, it is also found in cross-U type reactor that methanol reforming selectivity is the lowest due to the decreased water gas shift reaction under high temperature, thereby carbon monoxide concentration is increased. Furthermore, the reformed gas generated from the reactors is fed into a high temperature proton exchange membrane fuel cell (PEMFC). In the test of discharging for 4 h, the fuel cell fed by cross-U type reactor exhibits the most stable performance.

Transition metal-nitrogen complex have shown promising electrocatalytic activity towards the oxygen reduction reaction (ORR) that can potentially replace the platinum-based electrocatalysts in fuel cell, which generally suffer from scarcity and instability issue. Iron and cobalt have been reported to posses the best electrocatalytic performance in comparison with other transition metals due to the nature of their d-electron configuration that fulfill the prerequisite strong back-bonding for the activation of oxygen molecule. Apart from the metal active centre, other factors such as catalyst support, electrode thickness and surface-nitrogen content have also been considered play important roles to improve the catalytic performance of transition-metal-nitrogen complex materials. In this study we integrated those factors and approaches to create non-noble metal-based electrocatalysts for proton exchange membrane fuel cell (PEMFC) with improved catalytic activity. Iron and cobalt were used as ORR metal active centers and different type of carbon supports were employed as electrocatalysts supports. Three different electrocatalysts were developed in this project, including ironcobaltnitrogen complex supported carbon nanotubes that were grown on carbon paper substrate, iron-cobalt-nitrogen complex incorporated vertically aligned carbon nanotubes and iron-cobalt-nitrogen complex incorporated vertically aligned nitrogen-doped carbon nanotubes. The electrochemical performances of those electrocatalysts were compared with platinum-based electrocatalyst, which is the most common commercial electrocatalysts recently. The results show that the developed non-noble metal-based electrocatalysts posses improved electrocatalytic properties in terms of electrochemical surface area, electron transfer number, kinetic rate constant, durability and methanol fuel tolerance.

Tendo em vista a Economia do Hidrogênio e sua infinidade de possibilidades, este trabalho estuda a geração de hidrogênio utilizando a energia solar fotovoltaica. Tendo em vista o consumo mundial de energia crescente, novos métodos de produção energética tem que ser levados em consideração, como o fato do hidrogênio ser um vetor energético de baixo impacto ambiental. Por outro lado, as reservas de combustíveis fósseis não serão capazes de satisfazer essa demanda em longo prazo e seu uso contínuo produz efeitos colaterais, como a poluição que ameaça a saúde humana e os gases de efeito estufa associados à mudança climática. No contexto do Brasil, a eletrólise da água combinada com as energias renováveis e células a combustível seriam uma boa base para melhorar o fornecimento de energia distribuída. Propõe-se, no presente trabalho, produzir hidrogênio por energia renovável, especificamente pelo acoplamento direto de um gerador fotovoltaico a um eletrolisador alcalino de água experimental, concebido localmente. Busca-se entender as características inerentes da interação desses dispositivos, encontrar as eficiências de cada etapa do sistema montado, assim como a eficiência global, adquirindo uma noção mais precisa e prática do uso da energia solar fotovoltaica na alimentação de um eletrolisador. Os resultados experimentais evidenciaram que a transferência da energia do gerador fotovoltaico ao eletrolisador depende fortemente das condições instantâneas climáticas e do modo como estes estão conectados. A interdependência entre variáveis foi reproduzida pelas investigações com destaque para: densidade de corrente no eletrolisador, potencial elétrico, irradiância solar, concentração do eletrólito, área do eletrodo e dimensões da célula eletrolítica. A eficiência do eletrolisador alcançada foi de 21%. A eficiência global (irradiância solar - hidrogênio) foi de 2%. O presente estudo dá subsídios para que seja dimensionado o acoplamento do sistema eletrolisador - gerador FV a partir de uma célula eletrolítica buscando-se minimizar perdas. In view of the Hydrogen Economy and its endless possibilities, this work studies the hydrogen production using solar photovoltaic energy. With increasing global energy consumption, new methods of energy production have got to be taken into consideration, as hydrogen that it is an energy carrier with low environmental impact. On the other hand, fossil fuel reserves will not be able to meet this demand in the long term and its continuous use produces side effects such as pollution that threatens human health and greenhouse gases which are associated with climate change. For Brazilian energy context, electrolysis combined with renewable power source and fuel cell power generation would be a good basis to improve the distributed energy supply. It is proposed in this paper, to produce hydrogen by a direct coupling of a PV array with an experimental alkaline electrolyzer designed locally. It seeks to understand the inherent characteristics of the interaction of these energy forms, find the efficiencies of each step of the assembled system, as well as the global efficiency, acquiring a more precise notion and practice of the use of solar photovoltaic coupled with an electrolyzer. The experimental results showed that the transfer of energy from the PV array to the electrolyzer depends heavily on instant climatic conditions and how they are connected. The interdependence between variables was reproduced by the investigations, considering especially: current density, electric potential, solar irradiance, concentration of electrolyte, the electrode area and size of the electrolytic cell. The electrolyzer achieved an efficiency of 21%, approximately one-third of a commercial electrolyser efficiency. The overall efficiency (sol-hydrogen) was 2%. The present study gives subsidies to design an electrolyser PV generator system based on a given electrolytic cell seeking low losses.

In this paper, we demonstrate two novel green synthesis methods for preparing platinum-graphene catalysts for proton exchange membrane fuel cell (PEMFC) applications. Starting from graphite oxide, the platinum precursor is added and the composite is separately subjected to (a) focused solar radiation and (b) hydrogen gas, for carrying out simultaneous reduction of graphite oxide to graphene and platinum complexes to platinum nanoparticles. These co-reduction methods employ a single agent, namely either sunlight or hydrogen gas, to accomplish the reduction process. Both techniques are therefore cost and energy effective and capable of large scale production. Rotating disc electrode (RDE) and PEMFC measurements reveal the high performance of these electrocatalysts as compared to commercial Pt-C electrocatalysts due to high oxygen reduction reaction (ORR) activity. Stability studies show that both catalysts are highly stable under acidic medium. The proposed methods are quite general in their applicability and we believe that these can be extended for synthesizing a wide variety of electrocatalysts such as various metal, metal oxide or metal alloy nanoparticle decorated carbon nanostructures. � 2012 The Royal Society of Chemistry.

The high conductivity of graphene material (or its derivatives) and its very large surface area enhance the direct electron transfer, improving non-enzymatic electrochemical sensors sensitivity and its other characteristics. The offered large pores facilitate analyte transport enabling glucose detection even at very low concentration values. In the current review paper we classified the enzymeless graphene-based glucose electrocatalysts’ synthesis methods that have been followed into the last few years into four main categories: (i) direct growth of graphene (or oxides) on metallic substrates, (ii) in-situ growth of metallic nanoparticles into graphene (or oxides) matrix, (iii) laser-induced graphene electrodes and (iv) polymer functionalized graphene (or oxides) electrodes. The increment of the specific surface area and the high degree reduction of the electrode internal resistance were recognized as their common targets. Analyzing glucose electrooxidation mechanism over Cu-Co-and Ni-(oxide)/graphene (or derivative) electrocatalysts, we deduced that glucose electrochemical sensing properties, such as sensitivity, detection limit and linear detection limit, totally depend on the route of the mass and charge transport between metal(II)/metal(III); and so both (specific area and internal resistance) should have the optimum values. © 2022 by the authors. Licensee MDPI, Basel, Switzerland. Asst. Prof. Brouzgou, A., thankfully acknowledges the Research, Innovation and Excellence Structure (DEKA) of the University of Thessaly for the funding of the research program entitled: ‘Electrochemical (bio)sensors: synthesis of novel carbon monolayer-based nanoelectrodes for biomolecules detection’ and Ms Balkourani, G. (PhD student) thankfully acknowledges the Hellenic Foundation for Research and Innovation (HFRI), the PhD Fellowship grant. 25, 6816.