Rechargeable Zn-air batteries are under intensive studies because of their high-energy density, low cost, and safety. However, their wide application is prevented by several remaining technical issues, one of which is the lack of suitable bifunctional cathodic catalysts for oxygen reduction reaction (ORR) during discharging and oxygen evolution reaction (OER) during charging. Due to low material cost and wide distribution, carbon-based materials may serve as promising electrocatalysts, while doping heteroatoms such as nitrogen or boron can effectively enhance their catalytic activity. Herein, we pyrolyze a metal-organic framework containing Zn, N, and B as the precursor to synthesize dual-doped and metal-free porous carbon materials as efficient ORR/OER bifunctional electrocatalysts. The surface area of obtained carbon materials can be greatly enhanced by pyrolysis under H 2 -containing atmosphere. In addition, N and B are evenly distributed within the carbon materials due to the crystalline MOF precursor. The resultant carbon materials exhibit high ORR and OER catalytic activities in both half-cell and single-cell battery measurements. Our study has demonstrated for the first time that MOFs can be used as precursors to synthesize metal-free ORR/OER bifunctional cathodic electrocatalysts with great potential in rechargeable Zn-air batteries.

A metal-free ORR/OER bifunctional electrocatalyst derived from metal-organic frameworks for rechargeable Zn-Air batteries

In it for the long haul: Clusters of Pt nanowires (3D Pt nanoassemblies, Pt NA) serve as an electrocatalyst for low-temperature fuel cells. These Pt nanoassemblies exhibit remarkably high stability following thousands of voltage cycles and good catalytic activity, when compared with a commercial Pt catalyst and 20 % wt Pt catalyst supported on carbon black (20 % Pt/CB).

Self-Supported Interconnected Pt Nanoassemblies as Highly Stable Electrocatalysts for Low-Temperatur

To restore the natural nitrogen cycle (N-cycle), artificial N-cycle electrocatalysis with flexibility, sustainability, and compatibility can convert intermittent renewable energy (e.g., wind) to harmful or value-added chemicals with minimal carbon emissions. The background of such N-cycles, such as nitrogen fixation, ammonia oxidation, and nitrate reduction, is briefly introduced here. The discussion of emerging nanostructures in various conversion reactions is focused on the architecture/compositional design, electrochemical performances, reaction mechanisms, and instructive tests. Energy device advancements for achieving more functions as well as <i>in situ</i>/<i>operando</i> characterizations toward understanding key steps are also highlighted. Furthermore, some recently proposed reactions as well as less discussed C–N coupling reactions are also summarized. We classify inorganic nitrogen sources that convert to each other under an applied voltage into three types, namely, abundant nitrogen, toxic nitrate (nitrite), and nitrogen oxides, and useful compounds such as ammonia, hydrazine, and hydroxylamine, with the goal of providing more critical insights into strategies to facilitate the development of our circular nitrogen economy. 

https://www.sciopen.com/article_pdf/1531201054523838466.pdf

Recent advances in nanostructured heterogeneous catalysts for N-cycle electrocatalysis

https://doi.org/10.1016/j.xinn.2022.100281

Metal-organic framework nanocrystal-derived hollow porous materials: Synthetic strategies and emerging applications

In recent years, dual-atom catalysts (DACs) have attracted extensive attention, as an extension of single-atom catalysts (SACs). Compared with SACs, DACs have higher metal loading and more complex and flexible active sites, thus achieving better catalytic performance and providing more opportunities for electrocatalysis. This review introduces the research progress in recent years on how to design new DACs to enhance the performance of electrocatalysis. Firstly, the advantages of DACs in increasing metal loading are introduced. Then, the role of DACs in changing the adsorption condition of reactant molecules on metal atoms is discussed. Moreover, the ways in which DACs can reduce the reaction energy barrier of key steps and change the reaction path are explored. Catalytic applications in different electrocatalytic reactions, including the carbon dioxide reduction reaction, oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, and nitrogen reduction reaction are followed. Finally, a brief summary is made and the key challenges and prospects of DACs are introduced. 

Superiority of Dual‐Atom Catalysts in Electrocatalysis: One Step Further Than Single‐Atom Catalysts

https://onlinelibrary.wiley.com/doi/pdf/10.1002/smsc.202100010

Recent Advances on Electrospun Nanomaterials for Zinc–Air Batteries

Advanced Oxygen Electrocatalysis in Energy Conversion and Storage

Recent progress on advanced polymer-based electrolytes in zinc–air batteries

We report an amino-functionalized indium-organic framework for efficient CO2 reduction to formate. The immobilized amino groups strengthen the absorption and activation of CO2 and stabilize the active intermediates, which endow an enhanced catalytic conversion to formate despite the inevitable reduction and reconstruction of the functionalized indium-based catalyst during electrocatalysis. The reconstructed amino-functionalized indium-based catalyst demonstrates a high Faradaic efficiency of 94.4 % and a partial current density of 108 mA cm-2 at -1.1 V vs. RHE in a liquid-phase flow cell, and also delivers an enhanced current density of ca. 800 mA cm-2 at 3.4 V for the formate production in a gas-phase flow cell configuration. This work not only provides a molecular functionalization and assembling concept of hybrid electrocatalysts but also offers valuable understandings in electrocatalyst evolution and reactor optimization for CO2 electrocatalysis and beyond.

Efficient Electroconversion of Carbon Dioxide to Formate by a Reconstructed Amino-Functionalized Indium-Organic Framework Electrocatalyst.

Anion exchange membrane water electrolysis (AEMWE) with non-precious catalysts offers a promising route for industrial hydrogen production. However, the sluggish kinetics of anodic water oxidation hinder its efficiency and cost. We report herein a highly active two-dimensional trimetal–organic framework (NiCoFe–NDA) as a referential electrocatalyst for water oxidation. The as-prepared NiCoFe–NDA delivers a low overpotential of 215 mV at 10 mA cm−2 with a small Tafel slope of 64.1 mV dec−1 and exhibits excellent stability even at a high current density of 100 mA cm−2 for 50 h without obvious activity attenuation. A home-made AEMWE using an anodic NiCoFe–NDA catalyst affords a cell voltage of only 1.8 V to drive a current density of 325 mA cm−2 and performs robustly during continuous operation for over 100 h. During the anodic water oxidation, NiCoFe–NDA undergoes an in situ phase transformation, and the surface-reconstructed NiCoFe–NDA inherits its topological nanosheets and induces active surface-rich metal oxyhydroxides with abundant low-coordination catalytic environments, which would provide a positive multi-metal coupling effect to promote water oxidation. This work provides an organic–inorganic hybrid platform for designing high-efficiency electrocatalysts to advance water electrolysis technologies.

Chenfeng Xia

Papers

Recent Advances on Electrospun Nanomaterials for Zinc–Air Batteries

Advanced Oxygen Electrocatalysis in Energy Conversion and Storage

Recent progress on advanced polymer-based electrolytes in zinc–air batteries

Efficient Electroconversion of Carbon Dioxide to Formate by a Reconstructed Amino-Functionalized Indium-Organic Framework Electrocatalyst.

In situ ion-exchange preparation and topological transformation of trimetal–organic frameworks for efficient electrocatalytic water oxidation