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Proton transfer is a key step of the lithium-mediated electrochemical reduction of nitrogen to ammonia. Herein, we investigate the impact of the chemical nature of the proton carrier on the performance and highlight shuttles that enable effective ammonia synthesis.

Kinetics and coulombic efficiency of the electrochemical magnesium plating and stripping processes are to a significant extent defined by the composition of the electrolyte solution, optimization of which presents a pathway for improved performance. Adopting this strategy, we undertook a systematic investigation of the Mg

We report a new p-doping strategy for organic semiconductors with free radicals that enable reproducible enhancement in the conductivity and tuning of the work function. High efficiency and thermo-stability perovskite solar cells were achieved.

We demonstrate herein the fabrication of large-area (up to 30 cm2) organic-semiconductor-based films using slot-die coating – an established and highly scalable printing technology that enables deposition of uniform thin films on various substrates.

Metals are common electrocatalysts for N2-into-NH3 reduction. In protic media, H+ competes with N2 to be reduced into H2. NOx, common air pollutants, are predicted to be more selectively converted into NH3 than N2, and even more than H+ into H2.

The interpenetrating 2D-sheet framework of Co-TMBT-MOF cast onto nickel foam is used as a pre-catalyst to generate an efficient OER catalyst with low overpotential.

The activation of dinitrogen as a fundamental step in reactions to produce nitrogen compounds, including ammonia and nitrates, has a cornerstone role in chemistry. Bringing together research from disparate fields...

Electrocatalytic oxidation of ammonia is an appealing, low-temperature process for the sustainable production of nitrites and nitrates that avoids the formation of pernicious N2O and can be fully powered by renewable electricity. Currently, however, the number of known efficient catalysts for such a reaction is limited. The present work demonstrates that copper-based electrodes exhibit high electrocatalytic activity and selectivity for the NH3 oxidation to NO2− and NO3− in alkaline solutions. Systematic investigation of the effects of pH and potential on the kinetics of the reaction using voltammetric analysis andin situ Raman spectroscopy suggest that ammonia electrooxidation on copper occurrs via two primary catalytic mechanisms. In the first pathway, NH3 is converted to NO2− via a homogeneous electrocatalytic process mediated by redox transformations of aqueous [Cu(OH)4]−/2− species, which dissolve from the electrode. The second pathway is the heterogeneous catalytic oxidation of NH3 on the electrode surface favoring the formation of NO3−. By virtue of its nature, the homogeneous-mediated pathway enables higher selectivity and was less affected by electrode poisoning with the strongly adsorbed “N” intermediates that have plagued the electrocatalytic ammonia oxidation field. Thus, the selectivity of the Cu-catalyzed NH3 oxidation towards either nitrite or nitrate can be achieved through balancing the kinetics of the two mechanisms by adjusting the pH of the electrolyte medium and potential.

The instability and expense of anodes for water electrolyzers with acidic electrolytes can be overcome through the implementation of a cobalt-iron-lead oxide electrocatalyst, [Co-Fe-Pb]Ox , that is self-healing in the presence of dissolved metal precursors. However, the latter requirement is pernicious for the membrane and especially the cathode half-reaction since Pb2+ and Fe3+ precursors poison the state-of-the-art platinum H2 evolving catalyst. To address this, we demonstrate the invariably stable operation of [Co-Fe-Pb]Ox in acidic solutions through a cobalt-selective self-healing mechanism without the addition of Pb2+ and Fe3+ and investigate the kinetics of the process. Soft X-ray absorption spectroscopy reveals that low concentrations of Co2+ in the solution stabilize the catalytically active Co(Fe) sites. The highly promising performance of this system is showcased by steady water electrooxidation at 80±1 °C and 10 mA cm-2 , using a flat electrode, at an overpotential of 0.56±0.01 V on a one-week timescale.

Shuttling protons in ammonia synthesis An electrochemical route to ammonia could substantially lower the greenhouse gas emissions associated with the current thermal Haber-Bosch process. One relatively promising option under study involves reductive formation of lithium nitride, which can be protonated to ammonia. However, the ethanol used to date as a local proton source in these studies may degrade under the reaction conditions. Suryanto et al. report the use of a tetraalkyl phosphonium salt in place of ethanol (see the Perspective by Westhead et al. ). This cation can stably undergo deprotonation–reprotonation cycles and, as an added benefit, it enhances the ionic conductivity of the medium. Science , abg2371, this issue p. 1187 ; see also abi8329, p. 1149

Considering the attractive optoelectronic properties of metal halide perovskites (MHPs), their introduction to the field of photocatalysis was only a matter of time. Thus far, MHPs have been explored for the photocatalytic generation of hydrogen, carbon dioxide reduction, organic synthesis, and pollutant degradation applications. Of growing research interest and possible applied significance are the currently emerging developments of MHP-based Z-scheme heterostructures, which can potentially enable efficient photocatalysis of highly energy-demanding redox processes. In this Perspective, we discuss the advantages and limitations of MHPs compared to traditional semiconductor materials for applications as photocatalysts and describe emerging examples in the construction of MHP-based Z-scheme systems. We discuss the principles and material properties that are required for the development of such Z-scheme heterostructure photocatalysts and consider the ongoing challenges and opportunities in this emerging field.

Studies of the ammonia oxidation reaction (AOR) for the synthesis of nitrite and nitrate (NO

High intrinsic activity of oxygen evolution reaction (OER) catalysts is often limited by their low electrical conductivity. To address this, we introduce copper inverse opal (IO) frameworks offering a well-developed network of interconnected pores as highly conductive high-surface-area supports for thin catalytic coatings, for example, the extremely active but poorly conducting nickel-iron layered double hydroxides (NiFe LDH). Such composites exhibit significantly higher OER activity in 1 m KOH than NiFe LDH supported on a flat substrate or deposited as inverse opals. The NiFe LDH/Cu IO catalyst enables oxygen evolution rates of 100 mA cm

The large-scale deployment of proton-exchange membrane water electrolyzers for high-throughput sustainable hydrogen production requires transition from precious noble metal anode electrocatalysts to low-cost earth-abundant materials. However, such materials are commonly insufficiently stable and/or catalytically inactive at low pH, and positive potentials required to maintain high rates of the anodic oxygen evolution reaction (OER). To address this, we explore the effects of a dielectric nanoscale-thin layer, constituted of amorphous TiO

Ferroelectric semiconductors like BiFeO3 are increasingly being investigated for applications in solar energy conversion and storage due to their intrinsic ability to induce ferroelectric polarization-driven separation of the photogenerated charge carriers resulting in above-bandgap photovoltages. Nevertheless, the BiFeO3 has been commonly prepared using complex and expensive fabrication techniques, e.g., epitaxial growth, radio frequency sputtering and pulsed laser deposition, which are not economically viable for large-scale production. Herein, we report a facile and scalable method for the fabrication of porous perovskite BiFeO3 photoanodes, as well as sequential interfacial engineering methods to enhance their photoelectrochemical performance for water splitting. Upon atomic layer deposition of a TiO2 overlayer and photo-assisted electrodeposition of a cobalt oxide/oxyhydroxide co-catalyst, the photocurrent density of the engineered photoanode for oxygen evolution reaction (1 M NaOH) significantly increased from negligible photocurrent of the pristine BiFeO3 to 0.16 mA cm−2 at 1.23 V vs. reversible hydrogen electrode (RHE) under simulated 1 sun irradiation (100 mW cm−2, AM1.5G spectrum). Furthermore, such functionalization of the BiFeO3 photoanodes shifts the photoelectrochemical oxidation onset potential by 0.7 V down to 0.6 V vs. RHE. The significantly enhanced photoelectro-oxidation activity is facilitated by the improved charge transfer and electrochemical kinetics.

Spontaneous enhancement of the photovoltaic performance of perovskite solar cells (PSCs) after aging has been reported, but the underlying reasons for such behavior are still under debate. Herein, we demonstrate that this spontaneous improvement effect accompanied by self-attenuation of hysteresis in the current-voltage characteristics is time- and temperature-dependent. Moreover, it is universal to PSCs based on a range of mixed-ion perovskites and coupled to different hole- and electron-transporting materials. Time-resolved confocal fluorescence microscopy and other characterization techniques suggest that the "self-healing" phenomenon is accompanied by the homogenization and enhancement of the charge extraction efficiency as well as suppressed recombination throughout cm

In addition to its use in the fertilizer and chemical industries

The results presented herein unambiguously demonstrate that neither nanoparticulate carbon-supported gold, nor bismuth powder are active catalysts for the electrocatalytic dinitrogen reduction, but...

As research on sustainable ammonia synthesis via electrochemical and photochemical N2 reduction progresses to include a wider variety of aqueous and aprotic electrolytes, 1H NMR spectroscopy is inc...

High efficiency and environmental stability are mandatory performance requirements for commercialization of perovskite solar cells (PSCs). Herein, efficient centimeter-scale PSCs with improved stability were achieved by incorporating an additive-free 2,2',7,7'-tetrakis[

Caesium silver bismuth halide double perovskites, in the first instance Cs2AgBiBr6, were recently introduced to the field of emerging photovoltaics as environmentally friendly, non-toxic and thermodynamically stable photoabsorber materials. However, the wide indirect bandgaps of these materials indicate the need for bandgap engineering and enhancing the light absorption to improve the photovoltaic performance. The present work demonstrates that this can be achieved via modification of the double perovskite with sulphide to obtain caesium silver bismuth sulphobromide materials, Cs2AgBiBr6−2xSx, which have been synthesised as pin-hole-free uniform films and systematically investigated herein. Notable enhancements in the intrinsic light absorption for 0 ≤ x ≤ 0.2 are demonstrated, as are the improvements by up to 50% in the photocurrent density of the corresponding thin-film solar cells. The devices based on the films with the nominal composition Cs2AgBiBr5.8S0.1 delivered a short-circuit current density of 3.0 ± 0.3 mA cm−2 and a power conversion efficiency of 1.9 ± 0.1% (cf. 2.1 ± 0.2 mA cm−2 and 1.3 ± 0.1%, respectively, for the control cells based on the sulphide-free Cs2AgBiBr6). Equally important, caesium silver bismuth sulphobromides demonstrate excellent stability against all common environmental stimuli, viz. heat, light, and humidity.

In situ experiments combining X-ray absorption spectroscopy (XAS) and electrochemistry have now become an indispensable tool for understanding the mechanisms of operation, structure, and the modes of degradation of electrocatalysts under operational conditions. Herein, the design of a gas- and liquid-tight spectroelectrochemical cell (SEC) and an experimental protocol for the simultaneous collection of high-quality XAS and electrochemical data are introduced. The effects of the working electrode, loading of active material, and X-ray damage are demonstrated and interpreted by an example of a well-known heterogenite-like cobalt oxide water oxidation catalyst. The SEC permitted reproducible X-ray absorption near edge structure to be collected with a resolution of at least 0.05 eV (equivalent to approximately 0.02 unit oxidation state sensitivity) and allowed X-ray-mediated photoeffects to be examined in detail. Furthermore, tracking of the potential-dependent changes in the oxidation state of a cobalt oxide catalyst with high precision and reproducibility is demonstrated. These in situ XAS data are correlated with a previous detailed electrokinetic analysis to identify the nature of the active state of the heterogenite-like water oxidation catalyst and conclude that metal oxidation states higher than IV are not involved in the catalytic mechanism. Finally, the implications of the significantly different timescales of the probed electron transfer events and the XAS analysis on the interpretation of the in situ spectroelectrochemical data are critically discussed, focusing on the mechanism of the water oxidation reaction.

Electrochemical water splitting in acidic conditions offers important advantages over that in alkaline systems, but the technological progress is limited by the lack of inexpensive and efficient anode catalysts that can stably operate at a low pH and elevated temperature. Here we demonstrate oxygen evolution catalysts that are based on non-noble metals, are formed in situ during electrooxidation of acidic water and exhibit a high stability in operation due to a self-healing mechanism. The highly disordered mixed metal oxides generated from dissolved cobalt, lead and iron precursors sustain high water oxidation rates at reasonable overpotentials. Moreover, utilizing a sufficiently robust electrode substrate allows for a continuous water oxidation at temperatures up to 80 °C and rates up to 500 mA cm−2 at overpotentials below 0.7 V with an essentially flat support and with no loss in activity. This robust operation of the catalysts is provided by the thermodynamically stable lead oxide matrix that accommodates homogeneously distributed catalytic dopants. Electrochemical water splitting in acidic conditions is limited by the lack of inexpensive and stable anode catalysts. Now, Simonov and colleagues report a non-noble metal-based oxygen evolution catalyst formed in situ that exhibits high stability for acidic water oxidation due to a self-healing mechanism.

Ammonia is a widely produced chemical that is the basis of most fertilisers. However, it is currently derived from fossil fuels and there is an urgent need to develop sustainable approaches to its production. Ammonia is also being considered as a renewable energy carrier, allowing efficient storage and transportation of renewables. For these reasons, the electrochemical nitrogen reduction reaction (NRR) is currently being intensely investigated as the basis for future mass production of ammonia from renewables. This Perspective critiques current steps and miss-steps towards this important goal in terms of experimental methodology and catalyst selection, proposing a protocol for rigorous experimentation. We discuss the issue of catalyst selectivity and the approaches to promoting the NRR over H2 production. Finally, we translate these mechanistic discussions, and the key metrics being pursued in the field, into the bigger picture of ammonia production by other sustainable processes, discussing benchmarks by which NRR progress can be assessed. The electrochemical reduction of nitrogen is being intensely investigated as the basis for future ammonia production. This Perspective critiques current steps and missteps towards this goal in terms of experimental methodology and catalyst selection, proposing a protocol for rigorous experimentation.