Probing Nitrogen‐Doping Effects in the Core‐Shell Structured Catalysts for Bifunctional Electrocatalysis

Facile construction of S-containing Co-based metal organic framework core-shell microspheres as an efficient bifunctional oxygen electrocatalyst

A cost-effective non-noble metal bifunctional electrocatalyst towards the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) is very important for energy-related applications. Micro/nanomaterials with core-shell structures have emerged as potential non-noble metal catalyst candidates. Herein, an efficient bifunctional oxygen electrocatalyst, S-containing Co-based metal organic framework core-shell microspheres (Co-MOF-CSMSs), has been designed and constructed by using 2,2':5',2''-terthiophene-5,5''-dicarboxylic acid as a novel ligand through a facile one-step hydrothermal method. Due to the integrated favorable structural characteristics of the core-shell structure and MOFs for electrocatalysis, Co-MOF-CSMSs are revealed as a good bifunctional electrocatalyst for the ORR and OER, including an onset potential of 0.93 V vs. RHE (reversible hydrogen electrode), a half-wave potential of 0.78 V vs. RHE and an overpotential of 0.35 V at 10 mA cm^-2. This work provides a low-cost and facile method to design and construct advanced micro/nanomaterials with core-shell structures to targetedly develop high-performance bifunctional oxygen electrocatalysts.

Toward Efficient Carbon and Water Cycles: Emerging Opportunities with Single-Site Catalysts Made of 3d Transition Metals

Advances in the chemical and electrochemical transformation of carbon and water are vital for delivering affordable and environmentally friendly energy sources and chemicals. Central to this challenge is the performance of materials. Traditionally, noble metal particles or metal complexes have been used as catalysts for many reactions. Recently, 3d transition-metal single-site catalysts (3dTM-SSCs) have emerged as potentially transformational candidates for the next-generation high-performance noble-metal-free catalysts. Designing catalysts at the molecular level can lead to a more efficient utilization of metal atoms and at the same time enhance catalytic performance under harsh reaction conditions. Despite this promise, several fundamental issues remain, in particular the structural evolution of 3dTM-SSCs during the synthesis, the molecular-level insights into the structure of the active sites, catalytic mechanisms, and the long-term cycling stability. Here, the material chemistries that facilitate the 3dTM-SSCs generation through a controlled pyrolytic synthesis are discussed, with focus on elucidating the underlying performance descriptors that can tune the catalytic properties in various critical reactions in carbon and water cycles. The current challenges and possible solutions for improving these novel catalytic materials are also highlighted.

Interface and defect engineer of titanium dioxide supported palladium or platinum for tuning the activity and selectivity of electrocatalytic nitrogen reduction reaction

Electrocatalytic N₂ reduction reaction (NRR) under ambient condition is considered as an alternative and environmental-friendly technique to substitute the conventional process of Haber-Bosch for NH₃ production. However, there are still hurdles for researchers to control the balance between N₂ activation and competitive hydrogen evolution reaction (HER) to obtain high selectivity of NRR. Herein, we synthesized Pt/TiO₂ and Pd/TiO₂ hybrids by using laser ablation in liquid (LAL) technology combined with hydrothermal treatment and compared their activity and selectivity of N₂ reduction. The results concluded that Pt/TiO₂ exhibited a higher NH₃ yield rate whereas Pd/TiO₂ achieved a better FE for artificial N₂ fixation, confirming that enhanced activity surely needs more electrons and protons to participate in the reaction, but the limited protons and electrons furnishing could restrain HER activity and improve selectivity of NRR. Comparing with Pt/TiO₂, Pd/TiO₂ hybrids could serve as a superior catalyst for keeping a balance relationship between HER and NRR to realize excellent selectivity and high yield rate simultaneously in an alkaline solution. Overall, this work will provide a significant practice to rational design electrocatalysts for NRR at ambient conditions and Pd-based materials might open an electrocatalyst paradigm to solve the global energy and ecological crisis.