Xingquan He

A dopamine sensor based on a methoxypolyethylene glycol polymer covalently modified glassy carbon electrode

A dopamine (DA) sensor based on a methoxypolyethylene glycol (MPEG) polymer covalently modified glass carbon electrode (GCE) was fabricated by an electroadsorption method. The electrochemical behavior of the sensor towards the catalytic oxidation of DA in pH 5.0 phosphate buffer solution (PBS) was investigated by cyclic voltammetry. The modified electrode obviously enhanced the current response and decreased the overpotentials for the oxidation of DA. Using differential pulse voltammetry, the sensor gave a linear response to DA over the concentration range of 2.0-140 μM with a detection limit (S/N = 3) of 4.68 × 10(-8) M. It was found that MPEG can complex DA through hydrogen bonding interaction between ethylene oxide units of the polymer and the protonated dopamine in acidic PBS and preconcentrate it in the film, which improved the detection limit and sensitivity of DA. The DA sensor exhibits good sensitivity, selectivity and stability, and has been applied for the determination of DA in dopamine hydrochloride injection solution.

Tunable ternary (P, S, N)-doped graphene as an efficient electrocatalyst for oxygen reduction reaction in an alkaline medium

In this work, we utilize a one-step pyrolysis method to thermally synthesize phosphorus (P), sulfur (S) and nitrogen (N) ternary-doped graphene (PSNG) using graphene oxide (GO), phosphoric acid and thiourea precursors as a low-cost and highly-efficient catalyst for the oxygen reduction reaction (ORR). The synthesized PSNG was characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The electrocatalytic activity of the PSNG composite towards ORR was evaluated by the linear sweep voltammetry (LSV) method. Electrochemical measurements reveal that the pyrolyzed PSNG at 1 : 10 mass ratio of phosphoric acid to thiourea has excellent catalytic activity towards ORR in an alkaline electrolyte, including large kinetic-limiting current density and good stability as well as a desirable four-electron pathway for the formation of water. These superior properties make the PSNG a promising cathode catalyst for alkaline fuel cells.

Electrocatalytic activity of metalloporphyrins grown in situ on graphene sheets toward oxygen reduction reaction in an alkaline medium

A series of non-noble-metal catalysts for oxygen reduction reaction (ORR), based on metal 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin (M-THPP, M: Fe3+, Co2+, Ni2+, Mn2+) grown on poly(sodium-p-styrenesulfonate) modified reduced graphene oxide (PSS-rGO), were fabricated using an in situ solvothermal synthesis method. The morphology of the M-THPP/PSS-rGO was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Ultraviolet-visible (UV-vis) absorption spectroscopy and X-ray photoelectron spectroscopy (XPS) techniques were utilized to analyse the unusual interactions between the metalloporphyrins and graphene sheets. Electrochemical measurements using rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) techniques were employed to study the catalytic activity and the mechanism of the oxygen reduction reaction on the as-synthesised M-THPP/PSS-rGO catalysts in an alkaline medium. The half-wave potential for the ORR on the CoTHPP/PSS-rGO catalyst was found to be around −0.22 V vs. SCE, which was much higher than those on the other M-THPP/PSS-rGO catalysts and similar to that on Pt/C (−0.20 V vs. SCE). RDE and RRDE results show that the ORR process proceeds mainly via an almost 4-electron pathway on CoTHPP/PSS-rGO. The catalyst stability tests disclose that the CoTHPP/PSS-rGO is much more stable than the other M-THPP/PSS-rGO composites. The assembled CoTHPP/PSS-rGO catalyst possesses high activity, good long-term stability, excellent tolerance to the crossover effect of methanol and a facile 4-electron pathway for ORR, which could be used as a promising Pt-free catalyst in an alkaline direct methanol fuel cell.

Dopamine sensor development based on the modification of glassy carbon electrode with β-cyclodextrin-poly(N-isopropylacrylamide)

A stable electroactive film of β-cyclodextrin-poly(N-isopropylacrylamide) (CD-PNIPAM) was successfully prepared on a glassy carbon electrode (GCE) surface using an electroadsorption method for the determination of dopamine (DA). The electrochemical behavior of the fabricated sensor towards the catalytic oxidation of DA was investigated by a cyclic voltammetry (CV) method in pH 5.0 phosphate buffer solution. The CD-PNIPAM modified electrode exhibited a good electrocatalytic activity towards the oxidation of dopamine, and led to a significant decrease in the anodic overpotentials compared with bare GCE. Using a differential pulse voltammetry (DPV) method, the sensor gave a linear response to DA over the concentration range 0.1–60 μM with a detection limit (S/N = 3) of 3.34 × 10−8 M. The sensitivity of the sensor was 564.2 μA mM−1. It was found that CD-PNIPAM possessed an inclusive property resulting from the β-CD in the structure of the polymer and could form an inclusion complex with dopamine molecules by hydrogen bonding interactions, which improved the detection limit and sensitivity for DA. The proposed sensor exhibits good sensitivity, selectivity and stability and has shown potential for the determination of DA in real samples.

Fe9S10-decorated N, S co-doped graphene as a new and efficient electrocatalyst for oxygen reduction and oxygen evolution reactions

Nowadays, the hybrids of non-precious metal nanocrystals and heteroatom-doped graphene have been intensively researched as efficient electrocatalysts for the oxygen reduction reaction (ORR) in energy conversion and storage. Herein, a novel hybrid comprising Fe9S10 anchored onto nitrogen and sulfur dual-doped graphene (Fe9S10/N,S-G) was obtained via a two-step method, namely a π–π assemble process of p-phenyl-bis(3,4-dicyanophenyl) thioether iron polyphthalocyanine (PTFePPc) and graphene oxide and a pyrolysis procedure. It is worth noting that the Fe9S10/N,S-G obtained at 700 °C facilitated a direct four-electron catalytic pathway toward ORR with a low yield of hydrogen peroxide, favored a quick kinetic process with a small Tafel slope of 49 mV dec−1 for its decent ORR activity, and achieved excellent operational stability in an alkaline medium. Furthermore, the proposed electrocatalyst also favored good OER performance, comparable with the benchmark RuO2. The superior electrocatalytic activity of the composite is mainly attributed to the electronic coupling between nitrogen and sulfur atoms doped in the graphene, the highly active sites of Fe9S10 and Fe–N, and the synergistic effects between Fe9S10 and N,S-G.

Nitrogen-doped graphene-supported Co/CoNx nanohybrid as a highly efficient electrocatalyst for oxygen reduction reaction in an alkaline medium

In this work, we utilize a one-step pyrolysis method to thermally synthesize a non-precious cobalt-based nitrogen-doped graphene (Co-NG) using graphene oxide (GO) and guanidine hydrochloride (GuHCl) with a small amount of CoCl2 precursor as a low-cost and highly efficient catalyst for the oxygen reduction reaction (ORR). The synthesized cobalt-based nitrogen-doped graphene (Co-NG) was characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The electrocatalytic activity of the Co-NG composite towards the ORR was evaluated using linear sweep voltammetry method. Electrochemical measurements reveal that the obtained Co-NG 850 composite has excellent catalytic activity towards the ORR in an alkaline electrolyte, including a large kinetic-limiting current density and good stability, as well as it exhibits the desirable four-electron pathway for the formation of water. These superior properties make the Co-NG 850 a promising cathode catalyst for alkaline fuel cells.

Spinel CoMn2O4 nanoparticles supported on a nitrogen and phosphorus dual doped graphene aerogel as efficient electrocatalysts for the oxygen reduction reaction

In this work, we present a novel hybrid composed of spinel CoMn2O4 nanoparticles and a N, P dual-doped graphene aerogel (CoMn2O4/NPGA). The CoMn2O4/NPGA is characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The electrocatalytic activity of the CoMn2O4/NPGA composite towards the ORR was assessed using a linear sweep voltammetry method. Rotating disk electrode (RDE) measurements show that the as-obtained CoMn2O4/NPGA shows excellent ORR activity in an alkaline medium comparable to the benchmark Pt/C catalyst. Electrochemical measurements reveal that the ORR on CoMn2O4/NPGA proceeds through an almost four-electron pathway. Simultaneously, the methanol tolerance and operational stability of CoMn2O4/NPGA toward the ORR are prominently higher than those of commercial Pt/C. All these conspicuous properties suggest that our proposed CoMn2O4/NPGA may be used as a prospective Pt-free catalyst in alkaline direct methanol fuel cells.

Nitrogen- and sulfur-doped carbon nanoplatelets via thermal annealing of alkaline lignin with urea as efficient electrocatalysts for oxygen reduction reaction

Nowadays, the development of metal-free oxygen reduction reaction (ORR) catalysts based on heteroatom-doped carbon materials has become one of the most attractive topics in fuel cells. Here, we describe a green one-step pyrolysis method for the synthesis of N and S dual-doped carbon nanoplatelets by using alkaline lignin (AL) as the C and S sources combining with urea as a nitrogen dopant. After carbonization at 900 °C, such a hybrid material (N–S–C 900) possesses an excellent electrocatalytic activity towards ORR in both alkaline and acidic media, which is superior to the benchmark Pt/C catalyst in terms of the half-wave potential and diffusion-limiting current density in an alkaline medium. Meanwhile, the obtained hybrid also shows better stability and excellent methanol tolerance than the commercial Pt/C catalyst for ORR in both alkaline and acidic media. In particular, the N–S–C 900 has prominent operational stability in alkaline media, retaining 93.1% of the initial current density after 10 000 s. In this way, using natural biological resources provides a promising alternative to noble-metal catalysts.

Use of Cobalt Polyphthalocyanine and Graphene as Precursors to Construct an Efficient Co9S8/N,S-G Electrocatalyst for the Oxygen Electrode Reaction in Harsh Media

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are fundamental reactions connected with energy conversion and/or storage devices. However, the sluggish kinetics of the ORR and OER reduce the efficiency. To address these issues, the development of efficient and robust electrode catalysts is required desperately. Herein, a new Co9S8 nanocrystal hybrid anchored on a N‐ and S‐dual‐doped graphene (Co9S8/N,S‐G) was prepared by a two‐step method, namely, a π–π assembly process of p‐phenyl‐bis(3,4‐dicyanophenyl)thioether cobalt polyphthalocyanine (PTCoPPc) and graphene oxide and a pyrolysis procedure. Electrochemical studies demonstrated that Co9S8(800)/N,S‐G exhibited a comparable ORR performance with 20 wt % Pt/C, such as an onset potential and a half‐wave potential of 0.931 and 0.811 V vs. the reversible hydrogen electrode, respectively, a limiting current density of 5.207 mA cm−2, and a good long‐term stability with a current retention of 92.6 % after 10 000 s continuous measurements. Co9S8(900)/N,S‐G displayed an excellent OER activity, which was ascribed to the presence of pyridinic N, graphitic N, and the occupation of Co−N to catalyze the ORR; and the oxygen adsorption on the surface of Co9S8(900)/N,S‐G contributed significantly to the OER activity. The approach developed here offered a new strategy to construct efficient oxygen electrode catalysts.

An enhanced oxygen electrode catalyst by incorporating CoO/SnO2 nanoparticles in crumpled nitrogen-doped graphene in alkaline media

To address issues concerning energy consumption and the environment, it is of great importance to design a highly efficient, durable and inexpensive oxygen electrode for energy storage and conversion devices. In this work, CoO/SnO2 nanoparticles were successfully incorporated in nitrogen-doped graphene by a facile method. The composite was of porous structure, and exhibited efficient bifunctional activity and outstanding stability towards both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). For ORR, the catalyst favored a direct four-electron-transfer pathway, and produced kinetic current density values close to those of Pt/C. In addition, for OER, it achieved a lower overpotential at a current density of 10 mA cm−2 and a smaller Tafel slope than RuO2. What is more, the value of the potential difference ΔE(OER–ORR), a measure of the overall bifunctionality of the catalyst, was 0.72 V, comparable with the values for state-of-the-art nonprecious bifunctional catalysts. The remarkable bifunctional activity of the catalyst was mainly attributed to the synergistic effects between metal oxides and nitrogen-doped graphene.