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

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

Electrocatalytic oxygen reduction reaction (ORR) and oxygen evolution reduction (OER) are regarded as the key reactions via the sustainable system (fuel cell and water splitting), respectively. In OER, the transition from singlet oxygen species to triplet oxygen molecules is involved, meanwhile the ORR involves the transition from triplet oxygen molecules to singlet oxygen species. However, in these processes, the number of unpaired electrons is not conserved, which is not thermodynamically favorable and creates an additional energy barrier. Fortunately, regulating the electrocatalysis by spin-state modulation enables a unique effect on the catalytic performance, but the current understanding on spin-state engineering for electro-catalyzing ORR and OER is still insufficient. Herein, this review summarized the in-spin engineering for the state-of-the-art ORR and OER electrocatalysts. It began by introducing engineering of spin-state to eg filling for ORR and OER process, and then moved to spin polarization and spin-pinning effect for OER process. Various designed strategies focusing on how to regulate the spin-state of the active center have been summarized up. The connectivity of the structures of typical ORR (e.g. metal–nitrogen–carbon) and OER (e.g. design strategies oxides, metal organic frameworks) catalysts depending on the spin level is also discussed. Finally, we present the outlook from the aspects of template catalysts, characterization methods, regulation strategies, theoretical calculations, which will further expand the possibility of better electrocatalytic performance through spin-state modulation. This review concluded some open suggestions and prospects, which are worthy of the community’s future work.

Xiaoyu Zhang

Papers

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

MOF-Derived Materials for Energy Conversion

Electron spin modulation engineering in oxygen-involved electrocatalysis