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Effective water management is crucial for the optimal operation of low‐temperature polymer electrolyte membrane fuel cells (PEMFCs). Excessive liquid water production can cause flooding in the gas diffusion electrodes and flow channels, limiting mass transfer and reducing PEMFC performance. To tackle this issue, a nature‐inspired chemical engineering (NICE) approach has been adopted that takes cues from the integument structure of desert‐dwelling lizards for passive water transport. By incorporating engraved, capillary microchannels into conventional flow fields, PEMFC performance improves significantly, including a 15% increase in maximum power density for a 25 cm2 cell and 13% for a 100 cm2 cell. Electro‐thermal maps of the lizard‐inspired flow field demonstrate a more uniform spatial distribution of current density and temperature than the conventional design. Neutron radiography provides evidence that capillary microchannels in the lizard‐inspired flow field facilitate the efficient transport and removal of generated liquid water, thereby preventing blockages in the reactant channels. These findings present a universally applicable and highly efficient water management strategy for PEMFCs, with the potential for widespread practical implementation for other electrochemical devices. [ABSTRACT FROM AUTHOR]

The electrochemical reduction of CO2 (CO2RR) is a promising approach to maintain a carbon cycle balance and produce value‐added chemicals. However, CO2RR technology is far from mature, since the conventional CO2RR electrocatalysts suffer from low activity (leading to currents <10 mA cm−2 in an H‐cell), stability (<120 h), and selectivity. Hence, they cannot meet the requirements for commercial applications (>200 mA cm−2, >8000 h, >90 % selectivity). Significant improvements are possible by taking inspiration from nature, considering biological organisms that efficiently catalyze the CO2 to various products. In this minireview, we present recent examples of enzyme‐inspired and enzyme‐mimicking CO2RR electrocatalysts enabling the production of C1 products with high faradaic efficiency (FE). At present, these designs do not typically follow a methodical approach, but rather focus on isolated features of biological systems. To achieve disruptive change, we advocate a systematic design methodology that leverages fundamental mechanisms associated with desired properties in nature and adapts them to the context of engineering applications. [ABSTRACT FROM AUTHOR]

The electrocatalytic reduction reaction of carbon dioxide (CO2RR) has gained significant attention as a promising approach to mitigate carbon dioxide emissions and generate valuable chemicals and fuels. However, the practical application of CO2RR has been hindered by the lack of efficient and selective electrocatalysts, particularly to produce multi‐carbon (C2+) products. Nature serves as an ideal source of inspiration for the development of CO2RR electrocatalysts, as biological organisms can efficiently catalyze the same reaction and possess robust structures that are inherently scaling. In this review, recent advances in the nature‐inspired design of electrocatalysts for CO2RR to C2+ products are summarized and categorized based on their inspiration source, including the coordination sphere of metalloenzymes and the cascade reactions within the enzyme, as well as the local environment. The importance of understanding the fundamental mechanisms and the different contexts between nature and technological application in the design process is highlighted, with the aim to improve the nature‐inspired design of electrocatalysts for CO2RR to C2+ products. [ABSTRACT FROM AUTHOR]

We report a new one‐pot synthesis procedure for hierarchical zeolites with intracrystalline macropores and metal particles encapsulated within the zeolitic walls. The synthesis allows to prepare macroporous zeolites of MFI topology with different heteroatoms (silicalite‐1, ZSM‐5 and TS‐1) and different encapsulated noble metal particles, such as gold, platinum and palladium. The hierarchically structured zeolites contain large macropores with diameters around 400 nm, which are well distributed and interconnected and should significantly enhance mass transport properties. The encapsulation of metal nanoparticles within the zeolitic walls leads to remarkable sinter resistance of the particles. Encapsulated gold nanoparticles (2.6 nm) do not significantly change in size during an 18‐hour treatment at 600 °C under air, while non‐encapsulated gold particles sinter heavily during the same treatment. Catalytic experiments for the direct epoxidation of propene with hydrogen and oxygen show that both catalytic functions of a macroporous TS‐1 sample that encapsulates gold particles are accessible and active. This catalyst displays high activity, although PO selectivity could still be improved. These materials show great potential for use in catalytic applications, due to their bifunctional nature, high sintering resistance, shape selective properties and hierarchical structure. [ABSTRACT FROM AUTHOR]

A method is introduced to rapidly (<30 min) synthesize single metal nanoparticles with narrow size distribution in a simple way. It is based on the electrospraying of a metal precursor solution into a surfactant solution, which acts as a reducing and stabilizing agent. This synthesis method is demonstrated for the production of Ag and Au nanoparticles, which are incorporated onto carbonaceous and non-carbonaceous supports. The nanoparticle size depends on the internal diameter of the spraying nozzle. The removal of the stabilizing surfactant (dodecylamine; DDA) is also examined via thermal annealing and oxygen plasma treatments. Thermal annealing at a low temperature rate is found to be the most effective, as it completely removes DDA from the metal nanoparticles without inducing changes in their particle size. To verify that the supported Ag nanoparticles post calcination are surfactant-free and, thus, their surface sites are active, their oxygen reduction reaction (ORR) activity is measured in alkaline media, demonstrating similar values to the ones reported in the literature. [ABSTRACT FROM AUTHOR]

The active sites of catalysts can be tuned by using appropriate organic moieties. Here, we describe a facile approach to synthesise gold nanoparticles (AuNPs) using various Au(I) precursors. The core size of these AuNPs can be precisely tailored by varying the steric hindrance imposed by bound ligands. An interesting relationship is deduced that correlates the steric hindrance around the metal to the final size of the nanoparticles. The synthesised AuNPs are immobilised onto TS-1 zeolite (Au/TS-1) with minimal change in the final size of the AuNPs. The catalytic performance of Au/TS-1 catalyst is evaluated for the direct gas phase epoxidation of propylene with hydrogen and oxygen, an environmentally friendly route to produce propylene oxide. The results indicate that smaller AuNPs exhibit enhanced catalytic activity and selectivity. Furthermore, this synthetic approach is beneficial when tailored synthesis of gold nanoparticles of specific sizes is required. [ABSTRACT FROM AUTHOR]

Designing a stable and selective catalyst with high H2 utilisation is of pivotal importance for the direct gas‐phase epoxidation of propylene. This work describes a facile one‐pot methodology to synthesise ligand‐stabilised sub‐nanometre gold clusters immobilised onto a zeolitic support (TS‐1) to engineer a stable Au/TS‐1 catalyst. A non‐thermal O2 plasma technique is used for the quick removal of ligands with limited increase in particle size. Compared to untreated Au/TS‐1 catalysts prepared using the deposition precipitation method, the synthesised catalyst exhibits improved catalytic performance, including 10 times longer lifetime (>20 days), increased PO selectivity and hydrogen efficiency in direct gas phase epoxidation. The structure‐stability relationship of the catalyst is illustrated using multiple characterisation techniques, such as XPS, 31P MAS NMR, DR‐UV/VIS, HRTEM and TGA. It is hypothesised that the ligands play a guardian role in stabilising the Au particle size, which is vital in this reaction. This strategy is a promising approach towards designing a more stable heterogeneous catalyst. [ABSTRACT FROM AUTHOR]

The main obstacles toward further commercialization of electrochemical devices are the development of highly efficient, cost-effective and robust electrocatalysts, and the suitable integration of those catalysts within devices that optimally translate catalytic performance at the nanoscale to practically relevant length and time scales. Over the last decades, advancements in manufacturing technology, computational tools, and synthesis techniques have led to a range of sophisticated electrocatalysts, mostly based on expensive platinum group metals. To further improve their design, and to reduce overall cost, inspiration can be derived from nature on multiple levels, considering nature's efficient, hierarchical structures that are intrinsically scaling, as well as biological catalysts that catalyze the same reactions as in electrochemical devices. In this review, we introduce the concept of nature-inspired chemical engineering (NICE), contrasting it to the narrow sense in which biomimetics is often applied, namely copying isolated features of biological organisms irrespective of the different context. In contrast, NICE provides a systematic design methodology to solve engineering problems, based on the fundamental understanding of mechanisms that underpin desired properties, but also adapting them to the context of engineering applications. The scope of the NICE approach is demonstrated via this comparative state-of-the-art review, providing examples of bio-inspired electrocatalysts for key energy conversion reactions and nature-inspired electrochemical devices. [ABSTRACT FROM AUTHOR]

In the article "Nature-Inspired Electrocatalysts for CO2 Reduction to C2+ Products," the authors explore how the electroreduction of CO2 can be improved by drawing inspiration from nature. They discuss various factors that can enhance the selective electroreduction of CO2 to valuable products with two carbon atoms or more, such as metalloenzymes, cascade reactions, superhydrophobicity, and air-bubble collecting spiders. However, the authors emphasize the need for a systematic nature-inspired solution methodology rather than simply copying nature in order to achieve higher yields and stability. [Extracted from the article]

Hierarchical materials combining pore sizes of different length scales are highly important for catalysis and separation processes, where optimization of adsorption and transport properties is required. Nature can be an excellent guide to rational design, as it is full of hierarchical structures that are intrinsically scaling, efficient and robust. However, much of the “inspiration” from nature is, at present, empirical; considering the huge design space, we advocate a methodical, fundamental approach based on mechanistic features. [ABSTRACT FROM AUTHOR]

Hierarchische Nanomaterialien eignen sich hervorragend als Elektrokatalysatoren und Träger von Elektrokatalysatoren in Systemen für die elektrochemische Energieumwandlung. Die intrinsische Kinetik eines Elektrokatalysators wird von der Nanostruktur der aktiven Phasen und des Trägers bestimmt, während die Gesamteigenschaften auch von der Mesostruktur abhängen. Eine Kontrolle über diese beiden Strukturen ist demzufolge nötig. Es werden eine vergleichende Übersicht über die modernsten Katalysatoren und Träger sowie eine detaillierte Beschreibung von Synthesemethoden gegeben. Weitergehende Designverbesserungen bei hierarchischen Nanomaterialien erfordern die tiefgründige Erforschung des Zusammenhangs zwischen der Architektur der Materialien und ihrer Reaktions ‐ sowie Transportkinetik. Dafür können Vorbilder aus der Natur genutzt werden, die viele sehr effektive hierarchische Strukturen hervorgebracht hat. Die grundlegenden Kenntnis darüber, wie die begehrten Eigenschaften biologischer Systeme und ihre hierarchischen Architektur zusammenhängen, kann eine Basis für die Entwicklung neuartiger katalytischer Nanomaterialien und elektrochemischer Systeme nach dem Vorbild der Natur sein. Inspiration aus der Natur: Hierarchische Nanomaterialien sind geeignete Elektrokatalysatoren und Elektrokatalysatorträger in der elektrochemischen Energieumwandlung. Eine Voraussetzung für die weitere Verbesserung ihres Designs ist die genaue Erforschung des Einflusses der Architektur auf die Reaktions ‐ und Transportkinetik. Inspiration kann aus der Natur gezogen werden, die voller hierarchischer Strukturen ist. [ABSTRACT FROM AUTHOR]

Hierarchical nanomaterials are highly suitable as electrocatalysts and electrocatalyst supports in electrochemical energy conversion devices. The intrinsic kinetics of an electrocatalyst are associated with the nanostructure of the active phase and the support, while the overall properties are also affected by the mesostructure. Therefore, both structures need to be controlled. A comparative state-of-the-art review of catalysts and supports is provided along with detailed synthesis methods. To further improve the design of these hierarchical nanomaterials, in-depth research on the effect of materials architecture on reaction and transport kinetics is necessary. Inspiration can be derived from nature, which is full of very effective hierarchical structures. Developing fundamental understanding of how desired properties of biological systems are related to their hierarchical architecture can guide the development of novel catalytic nanomaterials and natureinspired electrochemical devices. [ABSTRACT FROM AUTHOR]

Micro-tomography (CT) can be successfully employed to characterize ex situ the structural changes occurring in graphite felt electrodes during vanadium redox flow battery (VRFB) operation. Coupled high resolution X-ray and electron microscopy in conjunction with XPS are used to elucidate the microstructural and chemical changes to the high voltage RFB carbon electrode. The results reveal the onset of corrosion of the carbon felt structure relatively early in the VRFB life-cycle, extended operation is expected to result in extensive microstructural evolution effects. [ABSTRACT FROM AUTHOR]

Carbon-tungsten oxide (C-WO3) and platinum/carbon-tungsten oxide (Pt/C-WO3) catalysts were prepared by chemical methods. The WO3 loading in the catalyst was 15 wt %. C-WO3 catalysts produced ∼60% less hydrogen peroxide than baseline C and Pt/C-WO3 electrocatalysts produced ∼30% less hydrogen peroxide formation than baseline Pt/C. Membrane electrode assemblies (MEAs) were prepared using Pt/C and Pt/C-WO3 electrocatalysts and subjected to accelerated durability tests at 90°C and 30% relative humidity (RH) at open circuit with hydrogen as fuel and oxygen as oxidant. The fluoride emission rate (in μmol F-/h-cm²) over 24 h was found to be reduced by ∼70% at the anode and ²60% at the cathode condensate when Pt/C-WO3 replaced Pt/C in the electrode. Fuel cell polarization data was obtained using Pt/C and Pt/C-WO3 in the cathode at 80°C and 75, 50, and 25% RH, with air and oxygen as oxidants and hydrogen as fuel. For all the test conditions, the performance of MEAs with Pt/C-WO3 was found to be lower than that of MEAs with Pt/C. Through electrochemical impedance spectroscopy experiments and polarization data analysis, the lower performance was attributed to (i) lower catalytic activity, and (ii) higher ionic and transport resistances in the electrodes. [ABSTRACT FROM AUTHOR]

Abstract: Pt/C/MnO2 hybrid catalysts were prepared by a wet chemical method. Pt/C electrocatalysts were treated with manganese sulfate monohydrate (MnSO4·H2O) and sodium persulfate (Na2S2O8) to produce MnO2. The presence of MnO2 was confirmed by FTIR spectroscopy. Rotating ring–disk electrode (RRDE) experiments were performed on electrodes prepared using the hybrid electrocatalysts to estimate the amount of hydrogen peroxide (H2O2) formed during the oxygen reduction reaction (ORR) as a function of MnO2 content. Pt/C/MnO2 (5% by weight of MnO2) hybrid electrocatalysts produced 50% less hydrogen peroxide than the baseline Pt/C electrocatalyst. The hybrid electrocatalysts were used to prepare membrane electrode assemblies that were tested at 90°C and 50% RH at open circuit with pure hydrogen as fuel and air as the oxidant. The fluoride ion concentration was measured using an ion selective electrode. The concentration of F− in the anode condensate over 24h was found to be reduced by a factor of 3–4 when Pt/C/MnO2 replaced Pt/C as the catalyst. Through cyclic voltammetry and RRDE kinetic studies, the lower ORR activity of the acid treated hybrid electrocatalysts was attributed to catalyst treatment with acid during MnO2 introduction. The activity of the hybrid catalyst was improved by switching to a water-based synthesis. [Copyright &y& Elsevier]

CeO2, Pt/CeO2and MnO2additives were found to lower the rate of free radical induced polymer electrolyte membrane degradation in an operating fuel cell by over one order of magnitude. [ABSTRACT FROM AUTHOR]

Review: 98 refs. [ABSTRACT FROM AUTHOR]

Review: [143 refs. [ABSTRACT FROM AUTHOR]

Intermittent switching between wet and dry reactant gases during operation in a polymer electrolyte fuel cell (PEFC) can improve performance stability, alleviating the effects of flooding by controlling the water content within the system. However, lifetime durability may be affected due to membrane electrode assembly (MEA) boundary delamination and membrane damage. Two relative humidity (RH) control strategies were investigated, using electrochemical performance and MEA degradation as critical indicators. It was found that intermittent switching between wet and dry gases does not accelerate fuel cell degradation if the duration of the dry gas period is set reasonably (dry gases stops before the voltage reaches the apex of the hump). Additionally, current and temperature distribution mapping was utilised to capture the dynamic response between these transitional stages. The switching of dry gases first makes the current density distribution homogeneous, and the maximum current density is reduced subsequently. Then, the current density near the inlet keeps decreasing. Intermittent switching between wet and dry reactant gases is easy to implement and overcomes limitations in mass transfer at medium and high current densities. • Long-term performance for intermittent RH control is compared to constant RH control. • TEM, XPS and SEM characterise Post-mortem MEAs to quantify the degradation. • Local dynamic response during gas switching is captured by current density mapping. [ABSTRACT FROM AUTHOR]