“We are here!” Oxygen functional groups in carbons for electrochemical applications

Heteroatom doping of carbon networks may introduce active functional groups on the surface of the material, induce electron density changes that alter the polarity of the carbon surface, promote the formation of binding sites for molecules or ions, or make the surface catalytically active for different reactions, among many other alterations. Thus, it is no surprise that heteroatom doping has become a well-established strategy to enhance the performance of carbon-based materials for applications ranging from water remediation and gas sorption to energy storage and conversion. Although oxygen functionalization is sometimes inevitable (i.e., many carbon precursors contain oxygen functionalities), its participation in carbon materials performance is often overlooked on behalf of other heteroatoms (mainly nitrogen). In this Mini-review, we summarize recent and relevant publications on the effect that oxygen functionalization has on carbonaceous materials performance in different electrochemical applications and some strategies to introduce such functionalization purposely. Our aim is to revert the current tendency to overlook it and raise the attention of the materials science community on the benefits of using oxygen functionalization in many state-of-the-art applications

Modulating between 2e^- and 4e^- pathway in the oxygen reduction reaction with laser-synthesized iron oxide-grafted nitrogen-doped carbon

In this study, we demonstrate the tuning of the oxygen reduction reaction (ORR) by iron/iron oxide nanoparticle grafted laser-patterned nitrogen-doped carbon (LP-NC) electrodes. Depending on the preparation route, i.e. addition of a molecular Fe(NO3)2 precursor before (route 1) or after pre-carbonization (route 2) of the citric acid / urea precursors, either the 4e- or the 2e- pathway in the ORR is facilitated leading to either H2O or H2O2 as a reaction product, respectively. The kinetic reaction conditions afford mixed valence metal oxide nanoparticles embedded in LP-NC in the form of either Fe2O3/Fe or Fe2O3/FeO/Fe, respectively, facilitated by an in situ carbothermal reduction during the laser-induced carbonization. In HR(S)TEM analysis we found evidence for the occurrence of Fe2O3 in the η- or α- phase, depending on the preparation route. Reciprocally, the graphitization is also affected by the preparation route leading to either homogeneous graphitization or locally a graphitized shell structures around the nanoparticles. In the 4e- mediated ORR facilitated by η-Fe2O3/Fe@LP-NC onset potentials as low as 0.70 V (vs. RHE) with a H2O2 production efficiency 4% and 10 % in alkaline and neutral electrolyte, respectively, were determined. On the other hand, α-Fe2O3/FeO/Fe@LP-NC present onset potentials for the 2e- mediated ORR is as low as 0.77 with a H2O2 production efficiency of nearly 80%

Green light photoelectrocatalysis with sulfur-doped carbon nitride : using triazole-purpald for enhanced benzylamine oxidation and oxygen evolution reactions

Novel high performing materials will dictate the pace of reinventing industrial chemical processes to attain desired carbon neutrality targets. Regarding the urgency of exploiting solar irradiation long range visible-light photoelectrocatalysts from abundant resources will play a key role in the aforementioned effort. Anionic doping via co-polymerization and pre-organization of precursors results in tuneable and extrinsic semiconductors, making this a highly attractive methodology. Triazole derivative-purpald, an unexplored precursor but sulfur (S) container, combined with melamine during one solid-state polycondensation reaction with two thermal steps leads to S-doped carbon nitrides (C34). The series of S-doped/CN4-based materials demonstrated enhanced optical, electronic, structural, geometric, textural, and morphological properties and exhibited higher performance in organic benzylamine photooxidation, oxygen evolution, and similar storing energy (capacitor brief investigation) than references. Among the five composites, 50M-50P exhibited the highest photooxidation conversion yield (84±3%) of benzylamine to imine at 535 nm – green light for 48h, due to an extra discrete shoulder reaching ~700 nm, an unusual high sulfur content, preservation of crystal size, new intraband energy states, rare deep structural defects by layer distortion, hydrophobic surface, low porosity, and 10-16 nm pores. An in-depth analysis of S doping was investigated coupling x-ray photoelectron spectroscopy, transmission electron microscope, and elemental analysis, providing insights on bonds, distribution, and surface/bulk content. This work contributes to the development of amorphous photocatalysts with long-visible-light range for solar energy conversion and storage

C₁N₁ thin films from guanine decomposition fragments

Polymeric semiconductors are finding a wide range of applications. In particular, graphitic carbon nitride g-C3N4 has been investigated extensively in the past decade. However, the family of carbon nitrides is not limited to C3N4 and new CXNY are now being explored due to their different bandgap energy, morphology, and overall physicochemical properties. Here, homogenous and semi-transparent C1N1 thin films are fabricated using guanine as a nontoxic molecular precursor. They are synthesized in a simplified chemical vapor deposition process on top of fused silica and fluorine doped tin oxide coated glass substrates. The chemical and structural studies reveal that C/N ratio is close to target 1, triazine vibrations are visible in vibrational spectra and stacking of the film is observed from glancing incidence X-ray diffraction data. The (photo)electrochemical properties are studied, the film is a p-type semiconductor with a good photoresponse to visible light and a suitable catalyst for hydrogen evolution reaction. A simple and safe way of synthesizing C1N1 films on a range of substrates is presented here