Effects of Surface Roughness and N-content on Oxygen Reduction Reaction Activity for the Carbon-based Catalyst Derived from Poultry Featherfiber

High-Efficiency Oxygen Reduction Reaction Revived from Walnut Shell

The development of inexpensive and efficient electrocatalysts for oxygen reduction reactions (ORR) remains a challenge with respect to renewable energy technologies. In this research, a porous, nitrogen-doped ORR catalyst is prepared using the hydrothermal method and pyrolysis with walnut shell as a biomass precursor and urea as a nitrogen source. Unlike past research, in this study, urea is not directly doped; instead, a new type of doping is carried out after annealing at 550 °C. In addition, the sample's morphology and structure are analyzed and characterized by scanning electron microscopy (SEM) and X-ray powder diffraction (XRD). A CHI 760E electrochemical workstation is used to test NSCL-900's performance in terms of oxygen reduction electrocatalysis (ORR). It has been found that the catalytic performance of NSCL-900 is significantly improved compared with that of NS-900 without urea doping. In a 0.1 mol/L KOH electrolyte, the half-wave potential can reach 0.86 V (vs. RHE) and the initial potential is 1.00 V (vs. RHE). The catalytic process is close to four-electron transfer and there are large quantities of pyridine nitrogen and pyrrole nitrogen.

Stable CuO with variable valence states cooperated with active Co2+ as catalyst/co-catalyst for oxygen reduction/methanol oxidation reactions

Catalysts/co-catalysts for cathodic oxygen reduction and anodic methanol oxidation reactions (ORR/MOR) play the major roles in promoting the commercialization of direct methanol fuel cells. Herein, bimetallic zeolite-imidazolate-frameworks (CoZn-ZIFs) is used as precursor to synthesize Co₃O₄@NPC/CuO composites as catalysts for ORR and Pt supports/co-catalysts for MOR. The ORR activity (E_1/2 = 0.83 V) and long-term stability (activity retention of 85.5% after 30,000 s) of Co₃O₄@NPC/CuO-400 (400 °C) dodecahedron are better than those of commercial Pt/C (10 wt%) in alkaline electrolytes. The surface CuO with variable valence states (Cu⁰ and Cu²⁺) can be used as both the active component for ORR and the protective layer for Co₃O₄ to enhance catalytic stability. Partial removal of CoO_x from carbon framework promotes the exposure of highly active sites (Co²⁺) on the Co₃O₄. For MOR, the mass activity of Pt-Co₃O₄@NPC/CuO-400 (5 wt%) (1947 mA mg_Pt^-1) is much higher than that of Pt/C (751 mA mg_Pt^-1), mainly attributing to that the Pt active sites are uniformly dispersed on Co₃O₄@NPC/CuO support. The strong interaction between Pt and CuO can reduce the bond strength of Pt-CO to enhance CO resistance. Co₃O₄ can activate H₂O molecules to provide sufficient OH^- species to promote MOR. This study provides a new idea for preparation of active ORR catalysts and MOR co-catalyst from bimetallic ZIFs.

Optimization Strategies of Preparation of Biomass-Derived Carbon Electrocatalyst for Boosting Oxygen Reduction Reaction: A Minireview

Oxygen reduction reaction (ORR) has attracted considerable attention for clean energy conversion technologies to reduce traditional fossil fuel consumption and greenhouse gas emissions. Although platinum (Pt) metal is currently used as an electrocatalyst to accelerate sluggish ORR kinetics, the scarce resource and high cost still restrict its further scale-up applications. In this regard, biomass-derived carbon electrocatalysts have been widely adopted for ORR electrocatalysis in recent years owing to their tunable physical/chemical properties and cost-effective precursors. In this minireview, recent advances of the optimization strategies in biomass-derived carbon electrocatalysts towards ORR have been summarized, mainly focusing on the optimization of pore structure and active site. Besides, some current challenges and future perspectives of biomass-derived carbon as high-performance electrocatalysts for ORR have been also discussed in detail. Hopefully, this minireview will afford a guideline for better design of biomass-derived carbon electrocatalysts for ORR-related applications.

Co-doped carbon materials synthesized with polymeric precursors as bifunctional electrocatalysts

The design of stable and high performance metal free bifunctional electrocatalysts is a necessity in alkaline zinc–air batteries for oxygen reduction and evolution reaction. In the present work co-doped carbon materials have been developed from polymeric precursors with abundant active sites to achieve bifunctional activity. A 3-dimensional microporous nitrogen–carbon (NC) and co-doped nitrogen–sulfur–carbon (NSC) and nitrogen–phosphorus–carbon (NPC) were synthesized using poly(2,5-benzimidazole) as an N containing precursor. The obtained sheet like structure shows outstanding ORR and OER performance in alkaline systems with excellent stability compared to Pt/C catalyst. The doped heteroatom in the carbon is expected to have redistributed the charge around heteroatom dopants lowering the ORR potential and modifying the oxygen chemisorption mode thereby weakening the O–O bonding and improving the ORR activity and overall catalytic performance. The bifunctional activity (ΔE = E_j=10 − E_1/2) of an air electrode for NPC, NSC, NC and Pt/C is 0.82 V, 0.87 V, 1.06 V and 1.03 V respectively, and the NPC value is smaller than most of the reported metal and non-metal based electrocatalysts. The ORR (from onset potential) and OER (10 mA cm⁻²) overpotential for NPC, NSC, and NC is (290 mV, 410 mV), (310 mV, 450 mV) and (340 mV, 600 mV) respectively. In the prepared catalyst the NPC exhibited higher ORR and OER activity (NPC > NSC > NC). The doping of P in NPC is found to have a great influence on the microstructure and therefore on the ORR and OER activity.

Metal free bifunctional catalysts based on co-doped carbon materials synthesized from polymeric precursors via a simple pyrolysis route with high cyclic stability and low polarization for Zn–air batteries.

KOH activation of coal-derived microporous carbons for oxygen reduction and supercapacitors

Due to the dilemma of rapid consumption of fossil fuels and environmental pollution, development of clean, efficient and renewable energy conversion and storage technology has become an urgent need. Supercapacitors and hydrogen-oxygen fuel cells as typical representatives have become the focus of scientific research, in which the electrode materials are of much importance to their improved activity. In this work, a series of porous carbons (PCs) with high specific surface areas were prepared using natural coals as carbon precursors coupled with KOH activation. The effects of the mass ratio of coal and KOH as well as different activation temperatures on the microstructures of the PCs and electrochemical properties were studied in detail. The optimal PC4 (KOH: coal = 4) possessed a high specific surface area (SSA) of 2092 m2 g-1 and a well-developed microporous structure. As the electrocatalyst, it exhibited a positive onset potential of 0.88 V (vs. reversible hydrogen electrode (RHE)) and half-wave potential of 0.78 V (vs. RHE) towards the oxygen reduction reaction (ORR) in an alkaline solution. PC4 also showed the highest specific capacitance of 128 F g-1 at a current density of 0.5 A g-1 among all the samples in this work. The relatively good performance of PC4 resulted from its well-developed microporous structure and large SSA, enabling fast mass transfer of electrolytes.

Preparation and optimization of activated nano-carbon production using physical activation by water steam from agricultural wastes

Production of activated nano-carbon from agricultural wastes was studied in this work. To obtain the optimum production conditions by a physical activation method, influence of temperature (850, 900, 950 and 1000 °C), activation residence time (30, 60 and 90 min), and mill rotation (200, 300 and 400 rpm) were investigated using three different raw materials including walnut, almond and pistachio shells. To prepare activated nano-carbon, all the samples were heated up to the final activation temperature under a continuous steam flow of 130 cm³ min⁻¹, and at a heating rate of 3 °C min⁻¹, and were held at the different activation temperatures for 30, 60 and 90 minutes. BET surface area of the obtained activated carbons was measured from nitrogen adsorption data in the relative pressure range between 0 to 1. Activated nano-carbon standard indexes were evaluated according to the ASTM standard and the samples were compared. First, the cellulose raw material was heated in the carbonization furnace at 600 °C and then activated in the advanced activation furnace at a temperature between 850 to 1000 °C for 30, 60 and 90 minutes with water vapor. Ash percentage, iodine content, moisture content, specific area, elemental analysis, and FESEM were used for product characterization. The results of the analysis showed that by using the water vapor physical activation method and optimizing the parameters of this process including time and rotation of the mill up to 10 min and 400 rpm, resulted in a significant increase in specific surface area, cavity volume and the iodine number of the final product.

Production of activated nano-carbon from agricultural wastes was studied in this work.

Chirality Induces the Self-Assembly To Generate a 3D Porous Spiral-like Polyhedron as Metal-Free Electrocatalysts for the Oxygen Reduction Reaction

The sluggish kinetics and large overpotential of the oxygen reduction reaction (ORR) severely limit the widespread production and application of metal-air batteries. Herein, a conductive three-dimensional (3D) porous spiral-like polyhedron structure composed of nitrogen-doped carbon nanosheets (L/D-SPNC) was utilized as catalysts with combination of 3D hierarchical porous properties and distinguishing intrinsic properties of two-dimensional (2D) nanosheets for ORR. The chiral template, l/d-tartaric acid, induces the self-assembly of the supramolecule and the formation of an orderly array of carbon with spiral-like surface feature on a molecular scale. The resulting L/D-SPNC exhibits a small wall thickness (2.5 nm), large specific surface area (2034.2 m²/g), and high conductivity (155.76 S/m), which indicates that the properties of 2D nanosheets building blocks are kept in 3D mode. As catalysts for ORR, the optimized L-SPNC-950-1 exhibits a more positive onset potential of 1.03 V compared with those of Pt/C (1.00 V) and a half-wave potential of 0.87 V is also comparable to those of Pt/C (0.87 V). Al-air battery discharge data demonstrate that the spiral-like structure facilitates the diffusion of the electrolyte and oxygen on a three-phase interface, causing weak polarization. Density functional theory (DFT) calculations prove that the twisted surface aggravates the differential charge distribution between C-C/C-N bonds.

Hierarchically structured carbon materials derived from lotus leaves as efficient electrocatalyst for microbial energy harvesting

Developing a highly efficient, cost-effective, easily scalable and sustainable cathode for oxygen reduction reaction (ORR) is a crucial challenge in terms of future "green" energy conversion technologies, e.g., microbial fuel cells (MFCs). In this study, a natural and widely available lotus leaf with intrinsically hierarchical structure was employed to serve as the single precursor to prepare the catalyst applied as the MFC cathode. The hierarchically particle-coated bio‑carbon was self-constructed from the lotus leaf, which yielded a large specific surface area, highly porous structure and superhydrophobicity via facile pyrolysis coupling hydrothermal activation by ZnCl₂/(NH₄)₂SO₄. Electrochemical evaluation demonstrated that these natural leaf-derived carbons have an efficient ORR activity. Specifically, the HC-900 catalyst with hydrothermal activation achieved an onset potential of -0.015 V vs. Ag/AgCl, which was comparable to the commercial Pt/C catalyst (-0.010 V vs. Ag/AgCl) and was more efficient than the DC-900 catalyst through direct pyrolysis. Furthermore, the HC-900 catalyst achieved an outstanding ORR activity via a one-step and four-electron pathway, exhibiting a potential alternative to Pt/C as electrocatalyst in ORR, due to its better long-term durability and methanol resistance. Additionally, the HC-900 catalyst was applied as an effective electrocatalytic cathode in an MFC system with a maximum power density of 511.5 ± 25.6 mW⋅m^-2, exhibiting a superior energy harvesting capacity to the Pt/C cathode.

Sustainable Carbonaceous Materials Derived from Biomass as Metal-Free Electrocatalysts

Although carbon is the second most abundant element in the biosphere, a large proportion of the available carbon resources in biomass from agriculture, stock farming, ocean fisheries, and other human activities is currently wasted. The use of sustainable carbonaceous materials as an alternative to precious metals in electrocatalysis is a promising pathway for transforming sustainable biomass resources into sustainable energy-conversion systems. The development of rational syntheses of metal-free carbonaceous catalysts derived from sustainable biomass has therefore become a topic of significant interest in materials chemistry. However, great efforts are still required to develop methods that are low cost, scalable, and environmentally friendly and which afford carbonaceous materials having an electrocatalytic performance comparable to, or even better than, existing precious metal catalysts. Herein, recent achievements in developing metal-free carbonaceous catalysts based on biomass are reviewed and discussed and the critical issues which still need to be addressed are highlighted. The focus is on representative synthesis and optimization strategies applicable to different kinds of biomass, as well as studies of the physicochemical structure and electrochemical performance of the resulting metal-free carbonaceous catalysts. Finally, some guidelines for the future development of this important area are provided.

Advanced Biomass-Derived Electrocatalysts for the Oxygen Reduction Reaction

Recent progress in advanced nanostructures synthesized from biomass resources for the oxygen reduction reaction (ORR) is reviewed. The ORR plays a significant role in the performance of numerous energy-conversion devices, including low-temperature hydrogen and alcohol fuel cells, microbial fuel cells, as well as metal-air batteries. The viability of such fuel cells is strongly related to the cost of the electrodes, especially the cathodic ORR electrocatalyst. Hence, inexpensive and abundant plant and animal biomass have become attractive options to obtain electrocatalysts upon conversion into active carbon. Bioresource selection and processing criteria are discussed in light of their influence on the physicochemical properties of the ORR nanostructures. The resulting electrocatalytic activity and durability are introduced and compared to those from conventional Pt/C-based electrocatalysts. These ORR catalysts are also active for oxygen or hydrogen evolution reactions.

Surficial nanoporous carbon with high pyridinic/pyrrolic N-Doping from sp3/sp2-N-rich azaacene dye for lithium storage

Dye to carbon: Two rationally designed pyridinic/pyrrolic N-doped porous carbons as anodic materials could be achieved by carbonizing π-conjugated azaacene dye born with high ratio sp³/sp²-N.