Huang Zhou

Keratin-derived S/N co-doped graphene-like nanobubble and nanosheet hybrids for highly efficient oxygen reduction

Heteroatom doped graphene-based materials generally offer great advantages towards constructing advanced catalysts. In this work, we develop a novel sulfur (S) and nitrogen (N) co-doped graphene-like nanobubble and nanosheet hybridized architecture prepared by a cost-efficient strategy using keratin containing abundant N and S sources as the precursor and KOH as the activating agent. After further graphitization and ammonia treatments at 1000 °C, it displays an ultrahigh surface area (1799 m2 g−1) as well as abundant active heteroatom dopants (graphitic-N, pyridinic-N and thiophene-S). Electrochemical measurements show that its onset potential is nearly 26 mV positive than that of the commercial Pt/C catalyst towards the oxygen reduction reaction (ORR) in alkaline media, and it has higher electrochemical stability and fuel tolerance than Pt/C. To the best of our knowledge, such ORR activity is the best one among the metal-free graphene-based catalysts in alkaline media, and much higher than that of the other reported biomass-derived carbon-based catalysts. Significantly, when employed as the air electrode for zinc–air batteries, this graphene-like hybrid catalyst displays an outstanding performance compared to the Pt/C catalyst. Moreover, compared with Pt/C, such a catalyst also exhibits comparable ORR activity and higher stability in acidic media. The outstanding ORR performance can be mainly attributed to its novel hybridized graphene-like architecture, which endows it with a similar thin layered property to graphene and an ultrahigh surface area as well as excellent hierarchical porous structures, and to the synergistic effect of the appropriate graphitization degree and high content of active heteroatoms.

Nitrogen-self-doped carbon with a porous graphene-like structure as a highly efficient catalyst for oxygen reduction

A non-noble metal nitrogen (N)-doped carbon catalyst, with a porous graphene-like structure, is prepared by pyrolyzing polyaniline with addition of urea. Herein, urea not only serves as a N source similar to polyaniline by incorporating N atoms into the carbon matrix, but plays a key role in forming the porous graphene-like structured carbon nanosheet. The electrochemical characterization shows that the prepared catalyst with a unique graphene-like structure exhibits an oxygen reduction reaction (ORR) activity that outperforms that of the commercial Pt/C catalyst in alkaline media, its half-wave potential nearly 30 mV more positive than Pt/C, and both superior stability and fuel (methanol and CO) tolerance to Pt/C. Significantly, such a catalyst also exhibits a good ORR activity which is comparable to Pt/C, as well as a higher stability than Pt/C in acidic media.

Facile Synthesis of Defect-Rich and S/N Co-Doped Graphene-Like Carbon Nanosheets as an Efficient Electrocatalyst for Primary and All-Solid-State Zn–Air Batteries

Developing facile and low-cost porous graphene-based catalysts for highly efficient oxygen reduction reaction (ORR) remains an important matter for fuel cells. Here, a defect-enriched and dual heteroatom (S and N) doped hierarchically porous graphene-like carbon nanomaterial (D-S/N-GLC) was prepared by a simple and scalable strategy, and exhibits an outperformed ORR activity and stability as compared to commercial Pt/C catalyst in an alkaline condition (its half-wave potential is nearly 24 mV more positive than Pt/C). The excellent ORR performance of the catalyst can be attributed to the synergistic effect, which integrates the novel graphene-like architectures, 3D hierarchically porous structure, superhigh surface area, high content of active dopants, and abundant defective sites in D-S/N-GLC. As a result, the developed catalysts are used as the air electrode for primary and all-solid-state Zn-air batteries. The primary batteries demonstrate a higher peak power density of 252 mW cm-2 and high voltage of 1.32 and 1.24 V at discharge current densities of 5 and 20 mA cm-2, respectively. Remarkably, the all-solid-state battery also exhibits a high peak power density of 81 mW cm-2 with good discharge performance. Moreover, such catalyst possesses a comparable ORR activity and higher stability than Pt/C in acidic condition. The present work not only provides a facile but cost-efficient strategy toward preparation of graphene-based materials, but also inspires an idea for promoting the electrocatalytic activity of carbon-based materials.

A self-template and KOH activation co-coupling strategy to synthesize ultrahigh surface area nitrogen-doped porous graphene for oxygen reduction

It is highly desirable but challenging to develop a facile strategy to synthesize nitrogen-doped porous graphene with ultrahigh surface area as well as advanced oxygen reduction activity to replace Pt based catalysts due to their high cost, stability and fuel crossover effect problems. Herein, a novel self-template strategy is developed to synthesize nitrogen doped porous graphene (NDPG) by using porous biomass with an abundant plate-like structure as a template, fully coupled with potassium hydroxide (KOH) activation, and followed by nitrogen doping by ammonia (NH3) injection. It is worth noting that, unlike the typical CVD method, during the synthesis process, no extra metal catalysts are introduced to form graphene. As a catalyst, the as-prepared NDPG exhibits outstanding ORR activity and stability. The half-wave potential is 10 mV higher than that of Pt/C in alkaline media and the stability is superior to Pt/C in both acidic and alkaline media. The superb catalytic performance of the formed graphene can be attributed to its mesoporous structure with an ultrahigh surface area (∼1969 m2 g−1) as well as the high electron conductivity of the graphene structure and efficient nitrogen content.

In Situ Derived Fe/N/S-Codoped Carbon Nanotubes from ZIF-8 Crystals as Efficient Electrocatalysts for Oxygen Reduction Reaction and Zinc-Air Batteries

Here we develop for the first time Fe/N/S-codoped carbon nanotubes (Fe/N/S-CNTs), derived from hydrazine hydrate and ferrous sulfate treated metal–organic frameworks, as an efficient ORR catalyst in both alkaline and acidic electrolytes. Hydrazine hydrate serves as a reducing agent to prevent the rapid aggregation of Fe nanocatalysts, which facilitates the growth of CNTs during pyrolysis. And it is discovered for the first time that sulfate ions can be used as a sulfur source to create C–S–C bonds by reaction with carbon at a high temperature. The prepared Fe/N/S-CNTs exhibits excellent ORR activity with a half-wave potential of 0.887 V in alkaline medium, which is 42 mV higher than that of commercial Pt/C (0.845 V), and its half-wave potential is just 26 mV lower than that of Pt/C in acidic medium. In addition, it also has high stability and methanol resistance ability in both alkaline and acidic electrolytes. Furthermore, when used as the cathode in primary Zn–air batteries, the power density of Fe/N/S-CNTs reaches 111 mW cm−2, which is 1.5 times higher than that of Pt/C (73 mW cm−2). Experimental results and DFT calculations demonstrate that the high-yield of CNTs, the optimal balance ratio of pyridinic and graphitic N, and the synergistic effect of C–S–C and Fe–Nx are all essential ingredients for the outstanding ORR performance.