Phosphorus-Doped Ordered Mesoporous Carbons with Different Lengths as Efficient Metal-Free Electrocatalysts for Oxygen Reduction Reaction in Alkaline Media

Phosphorus-doped ordered mesoporous carbons (POMCs) with different lengths were synthesized using a metal-free nanocasting method of SBA-15 mesoporous silica with different sizes as template and triphenylphosphine and phenol as phosphorus and carbon sources, respectively. The resultant POMC with a small amount of P doping is demonstrated as a metal-free electrode with excellent electrocatalytic activity for oxygen reduction reaction (ORR), coupled with much enhanced stability and alcohol tolerance compared to those of platinum via four-electron pathway in alkaline medium. Interestingly, the POMC with short channel length is found to have superior electrochemical performances compared to those with longer sizes

Fe-Treated Heteroatom (S/N/B/P)-Doped Graphene Electrocatalysts for Water Oxidation

Anodic water splitting is driven by hydroxide (OH^–) adsorption on the catalyst surface and consequent O₂ desorption. In this work, various heteroatoms (S/N/B/P) with different electronegativities and oxophilicities are introduced to alter the catalytic activity of reduced graphene oxide (RGO) as a catalyst for the oxygen evolution reaction (OER). It is found that, surprisingly, S-doped RGO outperforms the other RGOs doped with more electropositive or electronegative and more oxophilic heteroatoms, and this effect becomes more prominent after Fe treatment of the respective catalysts. Herein, we evaluate the OER activity of a series of Fe-treated mono-heteroatom (S/N/B/P)-doped RGO (Fe-X-G) catalysts, among which interestingly S-doped RGO catalyst treated with Fe (Fe-S-G) is found to show better OER activity than the well-known active Fe-N-C catalyst, demonstrating the best activity among all of the prepared catalysts, close to that of the state of the art IrO₂/C catalyst, along with pronounced long-term stability. Density functional theory (DFT) calculations indicate that the OER activity highly depends on the electroneutrality and oxophilicity of doped heteroatoms and doping-induced charge distribution over RGO, demonstrating that S with mediocre electronegativity and the least oxophilicity exhibits optimal free energy for the adsorption of the OER intermediate and desorption of the final OER product. Furthermore, it is found that Fe treatment greatly helps in enhancing the number of active sites through the regeneration of reduced catalytically active S sites and improving the conductivity and surface area of the S-doped RGO, which are found to be key factors to furnish the Fe-S-G catalyst with the capability to catalyze the OER with high efficiency, even though Fe is found to be absent in the final catalyst

N‑Doped Hierarchical Hollow Mesoporous Carbon as Metal-Free Cathode for Dye-Sensitized Solar Cells

In this study, novel nitrogen (N)-doped hollow core-mesoporous shell carbon (N-HCMSC) capsules with high surface area are synthesized by simple three-step processes and explored as metal-free counter electrode (CE) in comparison with undoped HCMSC in dye-sensitized solar cells (DSSCs). It is shown that N-HCMSC significantly improves the catalytic activity toward the reduction of both Co­(bpy)₃³⁺ and I₃^– due to much lower charge-transfer resistance (<i>R</i>_CT) at the CE/electrolyte interface. This is attributed not only to excellent surface properties including three-dimensionally interconnected hierarchical marco/mesoporosity with high surface area but also to N doping in N-HCMSC framework. Among various N species in the N-HCMSC framework, pyridinic and quaternary N species are considered to contribute significantly to the catalytic activity. In addition, N-HCMSC CE exhibits much better electrochemical stability than Pt CE toward both Co­(bpy)₃^2+/3+ and I^–/I₃^– redox reactions. The N-HCMSC enhances the cell efficiency and fill factor up to 8.76 and 77.6%, respectively, at one sun illumination and is readily applicable as a potential alternative of costly Pt-based CE for DSSCs with Y123-sensitized photoanodes