Biomimetic FeMo(Se, Te) as Joint Electron Pool Promoting Nitrogen Electrofixation.

It has been long believed that the FeMoS structure, where Fe is bonded with S, plays a pivotal role as a biomimetic catalyst for electrochemical nitrogen (N2 ) fixation. Nevertheless, the structure of Fe bonded to heavier analogues (Se or Te) has never been explored for N2 electrofixation. Here, we theoretically predict the electronic structure of FeMo(Se, Te) composed of tri-coordinated Fe species with open shells for binding with Se, which forms a joint electron pool for promoting N2 activation. Guided by this interesting prediction, we then demonstrate a two-step procedure to synthesize such structures, which display remarkable N2 electrofixation activities with an ammonia yield of 72.54 µg h-1 mg-1 and a Faradic efficiency of 51.67 % that are more than three times of the FeMoS counterpart. Further mechanism studies have been conducted by density function theory (DFT) simulations. This work provides new clues for designing versatile electrocatalytic materials for large-scale industrialization.

Single-zinc vacancy unlocks high-rate H2O2 electrosynthesis from mixed dioxygen beyond Le Chatelier principle.

Le Chatelier's principle is a basic rule in textbook defining the correlations of reaction activities and specific system parameters (like concentrations), serving as the guideline for regulating chemical/catalytic systems. Here we report a model system breaking this constraint in O2 electroreduction in mixed dioxygen. We unravel the central role of creating single-zinc vacancies in a crystal structure that leads to enzyme-like binding of the catalyst with enhanced selectivity to O2, shifting the reaction pathway from Langmuir-Hinshelwood to an upgraded triple-phase Eley-Rideal mechanism. The model system shows minute activity alteration of H2O2 yields (25.89~24.99 mol gcat-1 h-1) and Faradaic efficiencies (92.5%~89.3%) in the O2 levels of 100%~21% at the current density of 50~300 mA cm-2, which apparently violate macroscopic Le Chatelier's reaction kinetics. A standalone prototype device is built for high-rate H2O2 production from atmospheric air, achieving the highest Faradaic efficiencies of 87.8% at 320 mA cm-2, overtaking the state-of-the-art catalysts and approaching the theoretical limit for direct air electrolysis (~345.8 mA cm-2). Further techno-economics analyses display the use of atmospheric air feedstock affording 21.7% better economics as comparison to high-purity O2, achieving the lowest H2O2 capital cost of 0.3 $ Kg-1. Given the recent surge of demonstrations on tailoring chemical/catalytic systems based on the Le Chatelier's principle, the present finding would have general implications, allowing for leveraging systems "beyond" this classical rule.

Tandem-Parallel Electrochemical Cells to Produce Hydrogen Peroxide at Reduced Energy Consumption.

Large-scale industrialization of oxygen electroreduction requires producing hydrogen peroxide (H2O2) at large yield rates (current density >1 A cm-2, Faradic efficiency >95%). Under such vigorous reaction conditions, however, serious electric energy consumption (EEC) has been caused. According to the formula (EEC=Y×1000×R×F2172×FE2), a linear relationship can be identified between H2O2 yield rates (Y) and EEC, and therefore, achieving high yield rates (Y) while reducing EEC is very challenging in common electrochemical systems. In this work, we have designed a tandem-parallel oxygen electroreduction system composed of two oxygen electroreduction units. The tandem unit can effectively improve the Faradaic efficiency (FE) while the parallel section reduces total internal resistance (R). Consequently, the overall system can achieve a high H2O2 yield rate (592 mg h-1) with the lowest EEC (2.41 kWh kg-1) ever reported to the best of our knowledge. Further, the tandem-parallel system has shown promising stability by working for more than 10 cycles or 24 h. Besides oxygen electroreduction, other applications have been also demonstrated for the tandem-parallel system that can generate H2O2 for in situ degradation of rhodamine B pollutant.

Bioinspired inhibition of aggregation in metal-organic frameworks (MOFs).

Different from traditional procedures of using solid stabilizers like polymers and surfactants, here we demonstrate that water, as a very "soft" matter, could function as a "spacer" to prevent the aggregation of metal-organic frameworks (MOFs) in aqueous dispersions. Our theoretical calculations reveal in case of an excess of positively charged metal nodes of MOFs, where water molecules are ligated to metal nodes that greatly enhance MOFs' solution dispersibility through electrostatic stabilization. This discovery has motivated us to develop a facile experimental approach for producing a category of "clean" MOF dispersions without foreign additives. Potential application has been demonstrated for the size fractionation of MOFs, which results in small-size MOFs (50-80 nm) characteristic of superior electrocatalytic oxygen evolution activities (256 mV at 10 mA cm-2, Tafel slope of 49 mV dec-1 and durability >30 h). This work would provide new clues for aqueous processing of MOFs for many emerging applications.