Ammonia (NH3) is a globally important commodity for fertilizer production, but its synthesis by the Haber-Bosch process causes substantial emissions of carbon dioxide. Alternative, zero-carbon emission NH3 synthesis methods being explored include the promising electrochemical lithium-mediated nitrogen reduction reaction, which has nonetheless required sacrificial sources of protons. In this study, a phosphonium salt is introduced as a proton shuttle to help resolve this limitation. The salt also provides additional ionic conductivity, enabling high NH3 production rates of 53 ± 1 nanomoles per second per square centimeter at 69 ± 1% faradaic efficiency in 20-hour experiments under 0.5-bar hydrogen and 19.5-bar nitrogen. Continuous operation for more than 3 days is demonstrated.

Nitrogen reduction to ammonia at high efficiency and rates based on a phosphonium proton shuttle.

Metal-halide perovskites have been widely investigated in the photovoltaic sector due to their promising optoelectronic properties and inexpensive fabrication techniques based on solution processing. Here we report the development of inorganic CsPbBr3-based photoanodes for direct photoelectrochemical oxygen evolution from aqueous electrolytes. We use a commercial thermal graphite sheet and a mesoporous carbon scaffold to encapsulate CsPbBr3 as an inexpensive and efficient protection strategy. We achieve a record stability of 30 h in aqueous electrolyte under constant simulated solar illumination, with currents above 2 mA cm−2 at 1.23 VRHE. We further demonstrate the versatility of our approach by grafting a molecular Ir-based water oxidation catalyst on the electrolyte-facing surface of the sealing graphite sheet, which cathodically shifts the onset potential of the composite photoanode due to accelerated charge transfer. These results suggest an efficient route to develop stable halide perovskite based electrodes for photoelectrochemical solar fuel generation. While photoelectrochemical cells may offer access to solar fuels from a single integrated device, halide perovskite photoelectrodes are difficult to use due to their inherent moisture sensitivity. Here, the authors protect perovskite photoanodes with graphite sheets to boost their stability in water.

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Graphite-protected CsPbBr3 perovskite photoanodes functionalised with water oxidation catalyst for oxygen evolution in water

This review article presents and discusses the recent progress made in the stabilization, protection, improvement, and design of halide perovskite‐based photocatalysts, photoelectrodes, and devices for solar‐to‐chemical fuel conversion. With the target of water splitting, hydrogen iodide splitting, and CO2 reduction reactions, the strategies established for halide perovskites used in photocatalytic particle‐suspension systems, photoelectrode thin‐film systems, and photovoltaic‐(photo)electrocatalysis tandem systems are organized and introduced. Moreover, recent achievements in discovering new and stable halide perovskite materials, developing protective and functional shells and layers, designing proper reaction solution systems, and tandem device configurations are emphasized and discussed. Perspectives on the future design of halide perovskite materials and devices for solar‐to‐chemical fuel conversion are provided. This review may serve as a guide for researchers interested in utilizing halide perovskite materials for solar‐to‐chemical fuel conversion.

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Metal Halide Perovskites for Solar‐to‐Chemical Fuel Conversion

Ammonia and Nitric Acid Demands for Fertilizer Use in 2050

Electroreduction of nitrogen with almost 100% current-to-ammonia efficiency

An all-inorganic lead halide perovskite-based photocathode for stable water reduction.

Green production of NH 3 , especially Li-mediate electrochemical N 2 reduction reaction (NRR) in non-aqueous solutions, is attracting thronging research interest. Controversies on NRR mechanism greatly impedes its optimization and wide applications. To understand the electrocatalytic process, we treated Au coated carbon fibrous paper (Au/CP) as the model catalyst. In-situ XRD for the first time witnessed the transformation of lithium intermediates during NRR. Au greatly improved electron transfer kinetics to catalyze metallic Li formation, and accordingly highly accelerated NRR spontaneously. The Faradaic efficiency of NRR on Au/CP reached 34.0%, and NH 3 yield was as high as ~50 μg h -1 cm -2 . Our research proved that the key step of Li-mediate non-aqueous NRR is electrocatalytic Li reduction, and offered a novel electrocatalyst design method for Li reduction.

Domino effect: gold electrocatalyzing lithium reduction to accelerate nitrogen fixation


 High-entropy materials (HEMs) including high-entropy alloys (HEAs) and high-entropy ceramics (HECs) at nanoscale have promising prospects in many fields, yet a robust synthesis strategy is lacking. Herein, we present a simple and general approach, laser scanning ablation (LSA), to synthesize a vast library of HEA and HEC nanoparticles (NPs) including alloys, sulfides, oxides, borides, nitrides, phosphides. The LSA method takes only 5 nanoseconds per pulse to ablate the corresponding NPs precursors at atmospheric temperature and pressure in alkanes. The ultra-rapid process ensures up to 9 dissimilar metallic elements combined uniformly regardless of their thermodynamic solubility. As laser pulse precisely confines energy to desired microregions, the LSA method enables HEM NPs loading on various substrates, even thermally-sensitive ones such as metals and glass. Applied as electrocatalysts for overall water splitting, HEM NPs achieved an overpotential of 185 mV @ 10mA cm-2, which was among the best activities. The LSA technique discloses a large collection of new nanostructured HEMs with unique properties and attractive functions. We believe this general strategy will provide a versatile and flexible material platform for a wild range of fields such as biology, catalysis, electronics and magnetics.

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General synthesis of high-entropy alloy and ceramic nanoparticles in nanoseconds

Designing efficient oxygen evolution reaction (OER) electrocatalysts is essential for numerous sustainable energy conversion technologies. An obstacle that impedes the development of OER electrocatalysts is the insufficient emphasis on the spin attribution of electrons. Recently, the different spin configuration of reactants and products in the OER has been recognized as the factor that slows down the reaction kinetics. In this work, Mn substitution was introduced to LaCoO3, which brought about lattice expansion and reduced crystalline field splitting energy. This led to the increase in the effective magnetic moment, which triggers the transfer of Co3+ from low to higher spin states. Thus, the hybridization of Co eg and O 2p states across the Fermi level was strengthened. Specifically, with 25 at. % Mn substitution, LaCoO3 transits from a semiconductor to a half-metal, which benefits the spin-oriented electronic transport and resultantly promotes the OER. This method paves the way for the construction of spin pathways in catalysts.

Linfeng Gao

Papers

An all-inorganic lead halide perovskite-based photocathode for stable water reduction.

Domino effect: gold electrocatalyzing lithium reduction to accelerate nitrogen fixation

General synthesis of high-entropy alloy and ceramic nanoparticles in nanoseconds

Constructing spin pathways in LaCoO3 by Mn substitution to promote oxygen evolution reaction

Thiourea-assisted coating of dispersed copper electrocatalysts on Si photocathodes for solar hydrogen production