Biomass-derived carbon for ORR: pine needles as a single source for efficient carbon electrocatalyst

Polymerizable Ionic Liquid-Derived N, S co-Doped sp3/sp2 Carbon as Electrocatalyst for H2O2 Generation

The H2O2 generation via the green electrochemical process is of high interest. For the H2O2 electrochemical generation, the oxygen reduction reaction (ORR) is important. Unfortunately, the ORR is kinetically sluggish and catalysts are needed. However, noble metal ORR catalysts are pricy and scarcely applicable in applications. Therefore, non-precious metal catalysts are desired. Heteroatom-doped carbons show promise as metal-free ORR catalysts. The ORR catalytic activity will be enhanced by the carbon's sp2 and/or sp3 engineering. For N, S co-Cdoped and sp2/sp3 modulated carbon, a polymerizable ionic liquid of hydrolyzed vinyl imidazolium was studied. The carbon is studied as a metal-free catalyst for the ORR via the 2e- process. It is possible to get an onset potential of 0.88 V vs. RHE with approximately 50 % selectivity for the H2O2. The current study offers a simple technique for synthesizing heteroatom-doped sp2/sp3 designed carbon as catalysts for the electroreduction of O2 to produce H2O2, and a new way of tunning the sp3/sp2 carbon catalytic activity by modulating the ionic liquid.

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.

Cu-doped CaFeO3 perovskite oxide as oxygen reduction catalyst in air cathode microbial fuel cells

Cathode electrocatalyst is quite critical to realize the application of microbial fuel cells (MFCs). Perovskite oxides have been considered as potential MFCs cathode catalysts to replace Pt/C. Herein, Cu-doped perovskite oxide with a stable porous structure and excellent conductivity was successfully prepared through a sol-gel method. Due to the incorporation of Cu, CaFe_0.9Cu_0.1O₃ has more micropores and a larger surface area, which are more conducive to contact with oxygen. Doping Cu resulted in more Fe³⁺ in B-site and thus enhanced its binding capability to oxygen molecules. The data from electrochemical test demonstrated that the as-prepared catalyst has good conductivity, high stability, and excellent ORR properties. Compared with Pt/C catalyst, CaFe_0.9Cu_0.1O₃ exhibits a lower overpotential, which had an onset potential of 0.195 V and a half-wave potential of -0.224 V, respectively. CaFe_0.9Cu_0.1O₃ displays an outstanding four-electron pathway for ORR mechanism and demonstrates superiors corrosion resistance and stability. The MFC with CaFe_0.9Cu_0.1O₃ has a greater maximum power density (1090 mW m^-3) rather than that of Pt/C cathode (970 mW m^-3). This work demonstrated CaFe_0.9Cu_0.1O₃ is an economic and efficient cathodic catalyst for MFCs.

Green Crop Yam-Derived Carbons: Off-Plane Active Sites for Oxygen Electroreduction Identified by First-Principles

Plant-derived nonprecious metal catalysts are considered one of the promising candidates of platinum for oxygen reduction reaction (ORR). In this work, the typical microscopic morphology of fresh green crop yam is first detected by cryoscanning electronic microscopy. Using the green and widely sourced yam with spherical starch in nature as a precursor, well-defined spherical carbons are prepared via hypersaline-assisted hydrothermal carbonization and NH₃activation, featuring a high heteroatom doping level and a hierarchical porous structure. Experimental results and density functional theory (DFT) calculations reveal that diverse off-plane Fe-N_x-C_y ensembles on the spherical carbons trigger the high performance that exceeds state-of-art Pt/C and most reported carbon catalysts toward ORR in a KOH solution. The increased charge density and the bond length of Fe coordinated in the sites should be responsible for the significantly improved property. The easily editing of off-plane active sites from the simple carbon morphology may shed light on optimizing nonprecious carbons as next-generation catalysts for ORR.

Recent Advancements in the Synthesis and Application of Carbon-Based Catalysts in the ORR

Fuel cells are a promising alternative to non-renewable energy production industries such as petroleum and natural gas. The cathodic oxygen reduction reaction (ORR), which makes fuel cell technology possible, is sluggish under normal conditions. Thus, catalysts must be used to allow fuel cells to operate efficiently. Traditionally, platinum (Pt) catalysts are often utilized as they exhibit a highly efficient ORR with low overpotential values. However, Pt is an expensive and precious metal, posing economic problems for commercialization. Herein, advances in carbon-based catalysts are reviewed for their application in ORRs due to their abundance and low-cost syntheses. Various synthetic methods from different renewable sources are presented, and their catalytic properties are compared. Likewise, the effects of heteroatom and non-precious metal doping, surface area, and porosity on their performance are investigated. Carbon-based support materials are discussed in relation to their physical properties and the subsequent effect on Pt ORR performance. Lastly, advances in fuel cell electrolytes for various fuel cell types are presented. This review aims to provide valuable insight into current challenges in fuel cell performance and how they can be overcome using carbon-based materials and next generation electrolytes.