Ammonia (NH 3 ), one of the basic chemicals in most fertilizers and a promising carbon-free energy storage carrier, is typically synthesized via the Haber−Bosch process with high energy consumption and massive emission of greenhouse gases. The photo/ electrocatalytic nitrogen reduction reaction (NRR) under ambient conditions has attracted increasing interests recently, providing alternative routes to realize green NH 3 synthesis. Despite rapid advances achieved in this most attractive research field, the unsatisfactory conversion efficiency including a low NH 3 yield rate, and limited Faradaic efficiency or apparent quantum efficiency still remains as a great challenge. The NRR performance is intrinsically related to the electronic and surface structure of catalysts. Rational design and preparation of advanced catalysts are indispensable to improve the performance (e.g., activity and selectivity) of NRR. In this Review, various strategies for the development of desirable catalysts are comprehensively summarized, mainly containing the defect engineering, structural manipulation, crystallographic tailoring, and interface regulation. State-of-the-art heterogeneous NRR catalysts, prevailing theories and underlying catalytic mechanisms, together with current issues, critical challenges, and perspectives are discussed. It is highly expected that this Review will promote the understanding of recent advances in this area and stimulate greater interests for designing promising NRR catalysts in future.
Porosity and chirality are two of the most important properties for materials in the chemical and pharmaceutical industry. Inorganic microporous materials such as zeolites have been widely used in ion-exchange, selective sorption/separation and catalytic processes. The pore size and shape in zeolites play important roles for specific applications. Chiral inorganic microporous materials are particularly desirable with respect to their possible use in enantioselective sorption, separation and catalysis. At present, among the 179 zeolite framework types reported, only three exhibit chiral frameworks. Synthesizing enantiopure, porous tetrahedral framework structures represents a great challenge for chemists. Here, we report the silicogermanates SU-32 (polymorph A), SU-15 (polymorph B) (SU, Stockholm University) and a hypothetical polymorph C, all built by different stacking of a novel building layer. Whereas polymorphs B and C are achiral, each crystal of polymorph A exhibits only one hand and has an intrinsically chiral zeolite structure. SU-15 and SU-32 are thermally stable on calcination.
Simultaneous realization of improved activity, enhanced stability,a nd reduced cost remains ad esirable yet challenging goal in the search of oxygen evolution electrocatalysts in acid. Herein we report iridium-containing strontium titanates (Ir-STO) as active and stable,l ow-iridium perovskite electrocatalysts for the oxygen evolution reaction (OER) in acid. The Ir-STOc ontains 57 wt %l ess iridium relative to the benchmark catalyst IrO 2 ,b ut it exhibits more than 10 times higher catalytic activity for OER. It is shown to be among the most efficient iridium-based oxide electrocatalysts for OER in acid. Theoretical results reveal that the incorporation of iridium dopants in the STOm atrix activates the intrinsically inert titanium sites,s trengthening the surface oxygen adsorption on titanium sites and therebyg iving nonprecious titanium catalytic sites that have activities close to or even better than iridium sites.The oxygen evolution reaction (OER) is as luggish fourelectron/four-proton coupled reaction, but it is of practical significance for many (photo)electrochemical processes,such as fixation of dinitrogen and carbon dioxide as well as splitting water. Thei mprovement of OER electrocatalysis would enable higher overall efficiency for these important chemical processes.Hence,many efforts have been devoted to searching electrocatalytic materials that can mediate OER effi-ciently. [1] Thes tate-of-the-art electrocatalysts mainly include iron, cobalt, nickel-based bi-/multi-metallic (hydro)oxides with various types of crystalline/amorphous structures. [2] While these nonprecious OER electrocatalysts in alkaline media can exhibit stable catalytic activity comparable to,even higher than, that of IrO 2 ,t hey are operationally unstable in acidic media. At present, iridium-based metal oxides,such as IrO 2 ,a re still the only OER electrocatalysts with reasonable activity and stability in acid. Theextreme scarcity of iridium, together with the demands for OER electrocatalysis in acid, [3] has thus inspired much research to develop highly active,lowiridium electrocatalysts that can operate well in acidic conditions. [3,4] Despite recent efforts to explore low-iridium OER electrocatalysts working in acid, the progress is quite slow. Thei ridium content of the materials remains high, and correspondingly it is still difficult to realize the substantial improvement of iridium mass activity-one of the most important metrics for evaluating catalyst activity.A dditionally,s ome of the recently developed OER electrocatalysts often easily undergo serious surface reconstruction and even rapid deactivation during electrocatalysis in acidic media. [3,5] Therefore,d eveloping efficient oxygen evolution electrocatalysts that have good stability in acid and significantly lower iridium content is adesirable yet challenging goal.Herein we present iridium-containing strontium titanates as low-iridium electrocatalysts to mediate OER in acidic environment with high activity and good stability.T he material has am uch lower iridium co...
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