In-Situ Silica Xerogel Assisted Facile Synthesis of Fe-N-C Catalysts with Dense Fe-Nx Active Sites for Efficient Oxygen Reduction

Modulating the Energy Barrier via the Synergism of Cu3P and CoP to Accelerate Kinetics for Bolstering Oxygen Electrocatalysis in Zn-Air Batteries

Modulating the energy barrier of reaction intermediates to surmount sluggish kinetics is an utterly intriguing strategy for amplifying the oxygen reduction reaction. Herein, a Cu3P/CoP hybrid is incorporated on hollow porous N-doped carbon nanospheres via dopamine self-polymerization and high-temperature treatment. The resultant Cu3P/CoP@NC showcases a favorable mass activity of 4.41 mA mg-1 and a kinetic current density of 2.38 mA cm-2. Strikingly, the catalyst endows the aqueous Zn-air battery (ZAB) with a large power density of 209.0 mW cm-2, superb cyclability over 317 h, and promising application prospects in flexible ZAB. Theoretical simulations reveal that Cu functions as a modulator to modify the free energy of intermediates and adsorbs the O2 on the Co sites, hence rushing the reaction kinetics. The open and hydrophilic hollow spherical mesoporous structure provides unimpeded channels for reactant diffusion and electrolyte penetration, whereas the exposed inner and outer surfaces can confer a plethora of accessible actives sites. This research establishes a feasible design concept to tune catalytic activity for non-noble metal materials by construction of a rational nanoframework.

Regulating the frontier orbital of iron phthalocyanine with nitrogen doped carbon nanosheets for improving oxygen reduction activity

Iron phthalocyanine (FePc) has attracted widespread attention for its tunable electronic structure. However, the Fe-N sites suffer from undesirable oxygen reduction activity due to the symmetric geometries. A suitable substrate was thus needed to induce electron redistribution around Fe-N to improve the activity. Herein, ultrathin nitrogen-doped carbon nanosheets (N-CNSs) were prepared by a simple high temperature pyrolysis. Then iron phthalocyanine was loaded on the ultrathin nitrogen-doped carbon nanosheets (FePc@N-CNSs) by a low-cost and simple solution method. This composite catalyst shows an excellent ORR activity with a half potential of 0.88 V, an onset potential of 0.99 V and durability superior to commercial Pt/C. When used as an air cathode catalyst for rechargeable zinc-air batteries, FePc@N-CNS modified batteries outperform Pt/C + RuO2 modified batteries with higher power density and superior constant current charge-discharge cycling stability of 37 hours. The regulated electronic structure of FePc by the N-CNS substrate was revealed further by DFT calculations, which explained the enhanced adsorption of the active center to the intermediates and the increased ORR performance.

Silica-Derived Nanostructured Electrode Materials for ORR, OER, HER, CO2RR Electrocatalysis, and Energy Storage Applications: A Review

Silica-derived nanostructured catalysts (SDNCs) are a class of materials synthesized using nanocasting and templating techniques, which involve the sacrificial removal of a silica template to generate highly porous nanostructured materials. The surface of these nanostructures is functionalized with a variety of electrocatalytically active metal and non-metal atoms. SDNCs have attracted considerable attention due to their unique physicochemical properties, tunable electronic configuration, and microstructure. These properties make them highly efficient catalysts and promising electrode materials for next generation electrocatalysis, energy conversion, and energy storage technologies. The continued development of SDNCs is likely to lead to new and improved electrocatalysts and electrode materials. This review article provides a comprehensive overview of the recent advances in the development of SDNCs for electrocatalysis and energy storage applications. It analyzes 337,061 research articles published in the Web of Science (WoS) database up to December 2022 using the keywords "silica", "electrocatalysts", "ORR", "OER", "HER", "HOR", "CO2RR", "batteries", and "supercapacitors". The review discusses the application of SDNCs for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), carbon dioxide reduction reaction (CO2RR), supercapacitors, lithium-ion batteries, and thermal energy storage applications. It concludes by discussing the advantages and limitations of SDNCs for energy applications.

Mn-Doped Zn Metal-Organic Framework-Derived Porous N-Doped Carbon Composite as a High-Performance Nonprecious Electrocatalyst for Oxygen Reduction and Aqueous/Flexible Zinc-Air Batteries

Developing low-cost, efficient, and stable oxygen reduction reaction (ORR) electrocatalysts is crucial for the commercialization of energy conversion devices such as metal-air batteries. In this study, we report a Mn-doped Zn metal-organic framework-derived porous N-doped carbon composite (30-ZnMn-NC) as a high-performance ORR catalyst. 30-ZnMn-NC exhibits excellent electrocatalytic activity, demonstrating a kinetic current density of 9.58 mA cm-2 (0.8 V) and a half-wave potential of 0.83 V, surpassing the benchmark Pt/C and most of the recently reported non-noble metal-based catalysts. Moreover, the assembled zinc-air battery with 30-ZnMn-NC demonstrates high peak power densities of 207 and 66.3 mW cm-2 in liquid and flexible batteries, respectively, highlighting its potential for practical applications. The excellent electrocatalytic activity of 30-ZnMn-NC is attributed to its unique porous structure, the strong electronic interaction between metal Zn/Mn and adjacent N-doped carbon, as well as the bimetallic Mn/Zn-N active sites, which synergistically promote faster reaction kinetics. This work offers a controllable design strategy for efficient electrocatalysts with porous structures and bimetallic active sites, which can significantly enhance the performance of energy conversion devices.

Zn-Induced Synthesis of Porous Fe-N,S-C Electrocatalyst with Iron-Based Active Sites Containing Sulfides, Oxides and Nitrides for Efficient Oxygen Reduction and Zinc-Air Batteries

There is an urgent need to design and synthesize non-noble metal electrocatalysts (NNMEs) for the replacement of platinum-based electrocatalysts to enhance the sluggish oxygen reduction reaction (ORR) for Zn-air batteries and fuel cells. Herein, Fe-N,S-C materials were fabricated through two steps: first, reprecipitating hemin by adjusting the pH and, then, decorating it with melamine and cysteine in the presence of Zn2+. The resulting Fe-N,S-C-950 (Zn) was prepared after pyrolysis at 950 °C. Using this method, abundant iron-based active species with good dispersion were obtained. The fabrication of more micropores in Fe-N,S-C-950 (Zn) plays a positive role in the improvement of ORR activity. On comparison, Fe-N,S-C-950 (Zn) outperforms Fe-N,S-C-950 and Fe-N-C-950 (Zn) with respect to the ORR due to its larger specific surface area, porous structure, multiple iron-based active sites and N- and S-doped C. Fe-N,S-C-950 (Zn) achieves outstanding ORR performances, including a half-wave potential (E1/2) of 0.844 V and 0.715 V versus a reversible hydrogen electrode (RHE) in 0.1 M KOH and 0.1 M HClO4 solution, respectively. In addition, Fe-N,S-C-950 (Zn) shows an outstanding Zn-air battery performance with an open-circuit voltage (OCV) of 1.450 V and a peak power density of 121.9 mW cm-2, which is higher than that of 20 wt% Pt/C. As a result, the as-prepared electrocatalyst in this work shows the development of the Zn-assisted strategy combined with the assembly of porphyrins as NNMEs for the enhancement of the ORR in both alkaline and acidic solutions.

Novel Silica Hybrid Xerogels Prepared by Co-Condensation of TEOS and ClPhTEOS: A Chemical and Morphological Study

The search for new materials with improved properties for advanced applications is, nowadays, one of the most relevant and booming fields for scientists due to the environmental and technological needs of our society. Within this demand, hybrid siliceous materials, made out of organic and inorganic species (ORMOSILs), have emerged as an alternative with endless chemical and textural possibilities by incorporating in their structure the properties of inorganic compounds (i.e., mechanical, thermal, and structural stability) in synergy with those of organic compounds (functionality and flexibility), and thus, bestowing the material with unique properties, which allow access to multiple applications. In this work, synthesis using the sol-gel method of a series of new hybrid materials prepared by the co-condensation of tetraethoxysilane (TEOS) and 4-chlorophenyltriethoxysilane (ClPhTEOS) in different molar ratios is described. The aim of the study is not only the preparation of new materials but also their characterization by means of different techniques (FT-IR, ²⁹Si NMR, X-ray Diffraction, and N₂/CO₂ adsorption, among others) to obtain information on their chemical behavior and porous structure. Understanding how the chemical and textural properties of these materials are modulated with respect to the molar percentage of organic precursor will help to envisage their possible applications: From the most conventional such as catalysis, adsorption, or separation, to the most advanced in nanotechnology such as microelectronics, photoluminescence, non-linear optics, or sensorics.

Ultrathin Ru-Ni nanounits as hydrogen oxidation catalysts with an alkaline electrolyte

The development of hydrogen-oxygen fuel cells with an alkaline electrolyte was highly limited by the sluggish kinetics of the hydrogen oxidation reaction (HOR). Here, with a pyrolysis-reduction route, a new RuNi-based electrocatalyst was prepared, which presents an ultrathin nanowire-like structure. In alkaline media, this catalyst shows an excellent catalytic performance with an exchange current density of 1.10 mA cm^-2_disk for hydrogen oxidation. The exchange current density and mass activity of this catalyst are much higher than those of its single-metal counterparts and even the commercial Pt/C catalyst containing 20% Pt. Such a remarkable catalytic activity can be explained by the interaction between Ru and Ni; the incorporation of Ni may induce an electronic effect on the optimization of the Ru-H_ad strength and provide a functional surface that can absorb OH species, thus boosting the catalytic activity. These findings may cast a new light on the exploration of low-cost but high-efficiency catalysts for fuel cells.