Single oxygen-based advanced oxidation processes (1O2-AOPs) exhibit great prospects in selective degradation of organic pollutants. However, efficient production of 1O2 via tailored design of catalysts to achieve selective oxidation of contaminants remains challenging. Herein, we develop a simple strategy to regulate the components and coordination of Co-N-C catalysts at the atomic level by adjusting the Zn/Co ratio of bimetallic zeolitic imidazolate frameworks (ZnxCo1-ZIFs). Zn4Co1-C demonstrates 98% selective removal of phenol in the mixed phenol/benzoic acid (phenol/BA) solutions. Density functional theory calculations and experiments reveal that more active CoN4 sites are generated in Zn4Co1-C, which are beneficial to peroxymonosulfate activation to generate 1O2. Furthermore, the correlation between the origin of selectivity and well-defined catalysts is systematically investigated by the electron paramagnetic resonance test and quenching experiments. This work may provide novel insights into selective removal of target pollutants in a complicated water matrix.

Rational Regulation of Co-N-C Coordination for High-Efficiency Generation of 1O2 toward Nearly 100% Selective Degradation of Organic Pollutants.

The synergism of large surface area, multiscale porous structure, and good conductivity endows hierarchical carbon nanocages with high-level supercapacitive performances. Further nitrogen doping greatly improves the hydrophilicity, which boosts the supercapacitive performances to an ultrahigh specific capacitance of up to 313 F g(-1) at 1 A g(-1).

Hydrophilic hierarchical nitrogen-doped carbonnanocages for ultrahigh supercapacitive performance

Electrochemical N2 reduction (NRR) to ammonia is seriously limited by the competing hydrogen evolution reaction (HER), but atomic-scale factors controlling HER/NRR competition are unknown. Herein we unveil the mechanism, thermodynamics, and kinetics determining the HER/NRR efficiency on the state-of-the-art NRR electrocatalyst, Ru-N4, using grand canonical ensemble density functional theory (GCE-DFT). We show that NRR/HER intermediates coadsorb on the catalyst where NRR intermediates suppress HER and selectivity is determined by the initial step forming *NNH or *H. Our results provide crucial insight into the complex NRR/HER competition, show the necessity of using GCE-DFT calculations, and suggest ways to improve NRR selectivity. 

/pdf/coadsorption-of-nrr-and-her-intermediates-determines-the-21yxc7u4.pdf

Coadsorption of NRR and HER Intermediates Determines the Performance of Ru-N4 toward Electrocatalytic N2 Reduction

Electrochemical N2 reduction (NRR) to ammonia is seriously limited by the competing hydrogen evolution reaction (HER) but atomic-scale factors controlling HER/NRR competition are unknown. Herein we unveil the mechanism, thermodynamics, and kinetics determining the HER/NRR efficiency on the state-of-the-art NRR electrocatalyst, Ru-N4, using grand canonical ensemble density functional theory (GCE-DFT). We show that NRR/HER intermediates coadsorb on the catalyst where NRR intermediates suppress HER and selectivity is determined by the initial step forming *NNH or *H. Our results provide crucial insight into the complex NRR/HER competition, show the necessity of using GCE-DFT calculations, and suggest ways to improve NRR selectivity.

/pdf/coadsorption-of-nrr-and-her-intermediates-determines-the-1mczwatp.pdf

Coadsorption of NRR and HER intermediates determines the performance of Ru-N4 towards electrocatalytic N2 reduction

Solar-driven conversion of CO2 is considered an efficient way to tackle the energy and environmental crisis. However, the photocatalytic performance is severely restricted due to the insufficient accessible active sites and inhibited electron transfer efficiency. This work demonstrates a general in situ topological transformation strategy for the integration of uniform Co-based species to fabricate a series of multishelled superstructures (MSSs) for CO2 photocatalytic conversion. Thorough characterizations reveal the obtained MSSs feature ultrathin Co-based nanosheet assembled polyhedral structures with tunable shell numbers, inner cavity sizes, and compositions. The superstructures increase the spatial density of Co-based active sites while maintaining their high accessibility. Further, the ultrathin nanosheets also facilitate the transfer of photogenerated electrons. As a result, the ZnCo bimetallic hydroxide featuring an ultrathin nanosheet assembled quadruple-shell hollow structure (ZnCo-OH QUNH) exhibits high photocatalytic efficiency toward CO2 reduction with a CO evolution rate of 134.2 μmol h-1 and an apparent quantum yield of 6.76% at 450 nm. The quasi in situ spectra and theoretical calculations disclose that Co sites in ZnCo-OH QUNH act as highly active centers to stabilize the COOH* intermediate, while Zn species play the role of adsorption sites for the [Ru(bpy)3]2+ molecules. 

Ultrathin Nanosheet Assembled Multishelled Superstructures for Photocatalytic CO2 Reduction

Rational confinement engineering of MOF-derived carbon-based electrocatalysts toward CO2 reduction and O2 reduction reactions

Altering the spin state of Fe-N-C through ligand field modulation of single-atom sites boosts the oxygen reduction reaction

Fuel cells, metal–air batteries, and water splitting are energy conversion technologies that effectively deal with energy problems. The core reactions of these technologies include hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and carbon dioxide reduction reaction (CO2RR). This chapter reviews a series of MOFs-derived materials used in electrocatalytic reactions, including MOF-derived metal-dispersed single-atom carbon-based materials, MOF-derived metal nanoparticle carbon-based materials, MOF-derived nonmetallic heteroatom-doped carbon-based materials, etc. These materials retain the original advantages of MOF materials to a great extent, such as ultra-high porosity and specific surface area, and at the same time well overcome the common problems of poor conductivity and stability of MOFs, and provide new reaction sites. It expands the applicable response range and also provides convenience for performance optimization. These advantages make them have very efficient electrocatalytic activity and have a very broad prospect in the further research and application.

MOF-Derived Materials for Energy Conversion

Hydrogen has emerged as a green and sustainable fuel to meet the demand for future global energy. Distinct from steam reforming, electrochemical water splitting, especially powered by renewables, has been considered as a promising technique for scalable production of high-purity hydrogen with no carbon emission. Its commercialization depends on accelerating reaction kinetics and thus reduction of hydrogen cost, requiring catalysts that are efficient, economical, and capable of stable and sustained hydrogen production. Atomically dispersed metal carbon-based catalysts (ADMCs) have attracted extensive attention due to their high atom utilization, abundant accessible active sites, fast mass transfer, and well-defined and tunable structures as ideal models for commercialized hydrogen production catalysts. In this review, starting from the recently developed strategies of ADMCs synthesis, the microenvironment regulation of active sites of ADMCs are systematically summarized and discussed, such as atomically metal doping, synergetic atomically doping and ADMCs supported nanocrystals. With attention on the catalytic mechanisms and structure-activity relationships ranging from chemical coordination effects and electronic metal-support interaction, the active origin of ADMCs in the electrocatalytic hydrogen evolution reaction is discussed. Finally, the review outlooks the remaining challenges and emerging research topics in the future, including long service life, amplification preparation techniques, high-output alkaline water electrolysis, seawater electrolysis for hydrogen production and large current density hydrogen evolution. The new insights and knowledge into these aspects will be helpful for filling the existing gaps between scientific communities and industries and open up opportunities for bringing this promising technology into reality.

Su Jiang

Papers

Rational confinement engineering of MOF-derived carbon-based electrocatalysts toward CO2 reduction and O2 reduction reactions

Altering the spin state of Fe-N-C through ligand field modulation of single-atom sites boosts the oxygen reduction reaction

MOF-Derived Materials for Energy Conversion

Optimizing Atomically Dispersed Metal Electrocatalysts for Hydrogen Evolution: Chemical Coordination Effect and Electronic Metal Support Interaction.

Selecting appropriate model complexity: An example of tracer inversion for thermal prediction in enhanced geothermal systems