Bifunctional 3D n-doped porous carbon materials derived from paper towel for oxygen reduction reaction and supercapacitor

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.

A Review on Production and Surface Modifications of Biochar Materials via Biomass Pyrolysis Process for Supercapacitor Applications

Biochar (BC) based materials are solid carbon enriched materials produced via different thermochemical techniques such as pyrolysis. However, the non-modified/non-activated BC-based materials obtained from the low-temperature pyrolysis of biomass cannot perform well in energy storage applications due to the mismatched physicochemical and electrical properties such as low surface area, poor pore features, and low density and conductivity. Therefore, to improve the surface features and structure of the BC and surface functionalities, surface modifications and activations are introduced to improve its properties to achieve enhanced electrochemical performance. The surface modifications use various activation methods to modify the surface properties of BC to achieve enhanced performance for supercapacitors in energy storage applications. This article provides a detailed review of surface modification methods and the application of modified BC to be used for the synthesis of electrodes for supercapacitors. The effect of those activation methods on physicochemical and electrical properties is critically presented. Finally, the research gap and future prospects are also elucidated.

Engineering the electronic and strained interface for high activity of PdMcore@Ptmonolayer electrocatalysts for oxygen reduction reaction

Alloyed nanoparticles with core-shell structures provide a favorable model to modulate interfacial interaction and surface structures at the atomic level, which is important for designing electrocatalysts with high activity and durability. Herein, core-shell structured Pd₃M@Pt/C nanoparticles with binary PdM alloy cores (M = Fe, Ni, and Co) and a monolayer Pt shell were successfully synthesized with diverse interfaces. Among these, Pd₃Fe@Pt/C exhibited the best oxygen reduction reaction catalytic performance, roughly 5.4 times more than that of the commercial Pt/C catalyst used as reference. The significantly enhanced activity is attributed to the combined effects of strain engineering, interfacial electron transfer, and improved Pt utilization. Density functional theory simulations and extended X-ray absorption fine structure analysis revealed that engineering the alloy core with moderate lattice mismatch and alloy composition (Pd₃Fe) optimizes the surface oxygen adsorption energy, thereby rendering excellent electrocatalytic activity. Future researches may use this study as a guide on the construction of highly effective core-shell electrocatalysts for various energy conversions and other applications.

Recent progress in pyrolyzed carbon materials as electrocatalysts for the oxygen reduction reaction

This review reports some recent advances in pyrolytic carbon as an ORR catalyst and explores its structure–activity relationship.

Cu-MOF derived Cu–C nanocomposites towards high performance electrochemical supercapacitors

For the development of asymmetric supercapacitors with higher energy density, the study of new electrode materials with high capacitance is a priority. Herein, the electrochemical behavior of nano copper in alkaline electrolyte is first discovered. It is found that there are two obvious reversible redox symmetric peaks in the range of −0.8–0.2 V in the alkaline electrolyte, corresponding to the conversion of copper into cuprous ions, and then converting cuprous ions into copper ions, indicating that the nanocomposite electrode has the characteristics of a pseudocapacitive reaction. It has a specific capacitance of up to 318 F g⁻¹ at a current density of 1 A g⁻¹, which remains at nearly 100% after 10 000 cycles at the same current density. When assembled with a Ni(OH)₂-based electrode into an asymmetric supercapacitor, the device shows excellent capacitive behavior and good reaction reversibility. At 0.4 A g⁻¹, the supercapacitor delivers a reversible capacity of 8.33 F g⁻¹ with an energy density of 13.5 mW h g⁻¹. This study first discovers the electrochemical behavior of nano copper, which can provide a new research idea for further expanding the negative electrodes of supercapacitors with higher energy density.

A new Cu–C nanocomposite derived from Cu-based metal–organic framework exhibits greatly improved electrochemical performance.

A sandwich-like electron transport layer to assist highly efficient planar perovskite solar cells

Co-modification of an electron transport layer (ETL) with metal oxides and organic molecules can optimize the structure of the ETL and improve the performance of perovskite solar cells (PSCs). Here, a sandwich-structured ETL consisting of MgO/SnO2/EA was designed by co-modifying a SnO2 ETL with magnesium oxide (MgO) and ethanolamine (EA). The device with an ETL modified with MgO and EA has excellent performance in enhancing electron transport and blocking holes. It also inhibits the formation of deep defect states and improves the stability of the device. The introduction of MgO effectively improves the open-circuit voltage (VOC) of the device, while EA increases the short-circuit current density (JSC). The optimal efficiency of the PSC using the ETL co-modified with MgO and EA is 20.23%, which is much higher than that of the device with the unmodified SnO2 ETL (17.94%). The method described here provides an effective way to develop high performance ETLs co-modified with metal oxides and organic compounds for perovskite-based optoelectronic devices.

Macroscopic synthesis of ultrafine N-doped carbon nanofibers for superior capacitive energy storage

Carbon nanofibers (CNFs) with excellent electric conductivity and high surface area have attracted immense research interests in supercapacitors. However, the macroscopic production of CNFs still remains a great challenge. Herein, ultrafine N-doped CNFs (N-CNFs) with a diameter of ∼20 nm are synthesized through a simple and scalable sol-gel method based on the self-assembly of phenolic resin and cetyltrimethylammonium bromide. When employed in aqueous supercapacitors, the obtained activated N-CNFs manifest a high gravimetric/areal capacitance (380 F g^-1/1.7 F cm^-2) as well as outstanding rate capability and cycling stability. Besides, the activated N-CNFs also demonstrate excellent capacitive performance (330 F g^-1) in flexible quasi-solid-state supercapacitors. The remarkable electrochemical performance as well as the easy and scalable synthesis makes the N-CNFs a highly promising electrode material for supercapacitors.

Controlled synthesis of single cobalt atom catalysts via a facile one-pot pyrolysis for efficient oxygen reduction and hydrogen evolution reactions

Metal-nitrogen doped carbon catalysts (M-N/C) with abundantly accessible M-N_x sites, particularly single metal atom M-N/C (SAM-N/C), have been developed as a substitute for expensive Pt-based catalysts. These catalysts are used to increase the efficiency of otherwise sluggish oxygen reduction reactions (ORR) and hydrogen evolution reactions (HER). However, although the agglomerated metal nanoparticles are usually easy to form, they are very difficult to remove due to the protective surface-coating carbon layers, a factor that significantly hampers SAM-N/C fabrication. Herein, we report a one-step pyrolysis approach to successfully fabricate single cobalt atom Co-N/C (SACo-N/C) by using a Co²⁺-SCN^- coordination compound as the metal precursor. Thanks to the decomposition of Co²⁺-SCN^- compound at lower temperature than that of carbon layer deposition, Co-rich particles grow up to larger ones before carbon layers formation. Even though encapsulated by the carbon layers, it is difficult for the large Co-rich particle to be completely sealed. And thus, it makes the Co atoms possible to escape from incomplete carbon layer, to coordinate with nitrogen atoms, and to form SACo-N/C catalysts. This SACo-N/C exhibits excellent performances for both ORR (half-wave potential of 0.878 V) and HER (overpotential at 10 mA/cm² of 178 mV), and is thus a potential replacement for Pt-based catalysts. When SACo-N/C is integrated into a Zn-O₂ battery, battery with high open-circuit voltage (1.536 V) has high peak power density (266 mW/cm²) and large gravimetric energy density (755 mA h/g_Zn) at current densities of 100 mA/cm². Thus, we believe that this strategy may offer a new direction for the effective generation of SAM-N/C catalysts.

An efficient bifunctional electrocatalyst derived from layer-by-layer self-assembly of a three-dimensional porous Co-N-C@graphene

Three-dimensional (3D) porous carbon-based materials with tunable composition and microstructure are of great interest for the development of oxygen involved electrocatalytic reactions. Here, we report the synthesis of 3D porous carbon-based electrocatalyst by self-assembling Co-metal organic frameworks (MOF) building blocks on graphene via a layer-by-layer technique. Precise control of the structure and morphology is achieved by varying the MOF layer to tune the electrocatalytic properties. The as-produced electrocatalyst exhibits an excellent catalytic activity for the oxygen reduction reaction in 0.1 mol L^-1 KOH, showing a high onset potential of 0.963 V vs. reversible hydrogen electrode (RHE) and a low tafel slope of 54 mV dec^-1, compared to Pt/C (0.934 V and 52 mV dec^-1, respectively). Additionally, it shows a slightly lower potential vs. RHE (1.72 V) than RuO₂ (1.75 V) at 10 mA cm^-2 in an alkaline electrolyte. A rechargeable Zn-air battery based on the as-produced 3D porous catalyst demonstrates a high peak power density of 119 mW cm^-2 at a cell voltage of 0.578 V while retaining an excellent stability over 250 charge-discharge cycles.

Sustainable synthesis of novel carbon microwires for the modification of a Ti mesh anode in bioelectrochemical systems

Herein, an effective method was developed to integrate carbon microwires on Ti mesh (denoted as CM/TiM) to fabricate high-performance anodes with long-time stability in microbial fuel cell. CM/TiM was synthesized by colonizing filamentous fungi on the bread modified Ti mesh followed by carbonization, which could convert the attached mycelium into carbon microwires (denoted as CM). Benefiting from the biocompatibility and 3D interlaced structure of carbon microwires, the biomass accumulation (1027 ± 83 μg cm^-2) of CM/TiM have been significantly improved nearly 3 folds, thus the fabricated CM/TiM demonstrated 2-fold higher current density (12.19 ± 0.07 A m^-2) with significantly increased stability compared with TiM. Therefore, the present high power output, chemical stability and hydrophilic carbon microwires make CM/TiM stable, scalable and environmentally sustainable anodes in bioelectrochemical systems.

Reducing energy barriers of chemical reactions with a nanomicrocell catalyst consisting of integrated active sites in conductive matrices

Reducing energy barriers of chemical reactions is the never-ending endeavor of chemists. Inspired by the high reactivity of primary cells, we develop a nanosized fuel cell catalyst (denoted as nanomicrocell catalyst), consisting of integrated electrode pairs, conductive matrices and electrolytes, to improve the chemical reactivity. Specifically, the anodes are Pd species which is combining with the electron-rich N atoms in B-and-N co-doped carbon dots; the cathodes are electron-deficient B atoms; and the conductive matrices are B-and-N co-doped carbon dots which are connecting with the electrode pairs. Similar to the reactivity of primary cells, the catalytic properties of the nanomicrocell catalyst in hydrogenation of benzaldehyde are depending on the properties of electrode pairs, conductive matrices and electrolytes. The unique catalytic properties are attributed to the different substrate adsorption capability and catalytic properties of paired electrodes, and the easy migration of electrons and charge carriers, which could improve the synergetic effect between paired active sites. Therefore, this work may open up a new window for designed synthesis of advanced catalysts which could highly lower the energy barriers of chemical reactions.