Zhenrong Yang

Facile synthesis and excellent electrochemical properties of NiCo2O4 spinel nanowire arrays as a bifunctional catalyst for the oxygen reduction and evolution reaction

Developing catalysts with high electrocatalytic activity for an oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) has recently attracted much attention because the sluggish kinetics of these two reactions limits the performance and commercialization of fuel cells and metal–air batteries. Herein, a facile template-free co-precipitation route was reported for the design and fabrication of well-ordered NiCo2O4 (NCO) spinel nanowire arrays. The as-prepared NCO spinel nanowire arrays are characterized by XRD, SEM, TEM, BET and XPS. BET results show that NCO spinel nanowire arrays have a mesoporous (ca. 8 nm) structure and a high specific surface area of 124 m2 g−1. The catalytic activity of NCO spinel nanowire arrays for the ORR and the OER in 0.1 M KOH solution has been studied by using a rotating ring-disk electrode (RRDE) technique. RRDE results show that the NCO spinel nanowire array catalyst exhibits excellent catalytic activity for the ORR. The ORR mainly favors a direct four electron pathway, which is close to the behavior of the Pt/C (20 wt% Pt on carbon) electrocatalyst under the same testing conditions. Anodic linear scanning voltammogram results show that the NCO spinel nanowire array catalyst is more active for the OER. The chronoamperometric and cyclic voltammogram tests show that the NCO spinel nanowire array catalyst exhibits excellent stability and reversibility for the ORR and the OER.

Phosphorus-doped porous carbons as efficient electrocatalysts for oxygen reduction

Efficient electrocatalysts for the oxygen reduction reaction (ORR) play a critical role in the performance of fuel cells and metal–air batteries. In this study, we report a facile synthesis of phosphorus (P)-doped porous carbon as a highly active electrocatalyst for the ORR. Phosphorus-doped porous carbon was prepared by simultaneous doping and activation of carbon with phosphoric acid (H3PO4) in the presence of Co. Both phosphorus and cobalt were found to play significant roles in improving the catalytic activity of carbon for the ORR. The as-prepared phosphorus-doped porous carbon exhibited considerable catalytic activity for the ORR as evidenced by rotating ring-disk electrode studies. At the same mass loading, the Tafel slope of phosphorus-doped porous carbon electrocatalysts is comparable to that of the commercial Pt/C catalysts (20 wt% Pt on Vulcan XC-72, Johnson Matthey) with stability superior to Pt/C in alkaline solutions.

A facile synthesis of CoFe2O4/biocarbon nanocomposites as efficient bi-functional electrocatalysts for the oxygen reduction and oxygen evolution reaction

Efficient electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are crucial for improving the performance of metal–air batteries. In this study, CoFe2O4/biocarbon (CFO/BC) nanocomposites have been synthesized via a facile biosynthesis method by using yeast cells as carbon sources and structural templates. The as-prepared CFO/BC nanocomposites possess a hierarchical structure with a high surface area (79.84 m2 g−1). The rotating ring-disk electrode (RRDE) and rotating disk electrode (RDE) measurements revealed that CFO/BC nanocomposites exhibit excellent catalytic activity for both the ORR and OER. The onset potential of CFO/BC for the ORR is −0.14 V (vs. Ag/AgCl), which is higher than that of CoFe2O4 (−0.29 V) and that of biocarbon (−0.25 V), respectively. Meanwhile, the CFO/BC nanocomposites show much higher activity for the OER as compared to CoFe2O4 and biocarbon. The chronoamperometric tests show that the CFO/BC catalyst shows high durability for both the ORR and OER, outperforming the commercial Pt/C (20 wt% Pt on Vulcan XC-72, Johnson Matthey). The high electrocatalytic activity and durability of the CFO/BC nanocomposite are mainly attributed to the strong coupling between CoFe2O4 nanoparticles and biocarbon as well as the hierarchical structure of CFO/BC.

Facile Synthesis of Gold-Nanoparticle-Decorated Gd0.3Ce0.7O1.9 Nanotubes with Enhanced Catalytic Activity for Oxygen Reduction Reaction

We demonstrated a facile method to synthesize gold-nanoparticle-decorated Gd0.3Ce0.7O1.9 (Au-GDC) nanotubes. X-ray diffraction, transmission electron microscopy, X-ray photoelectron microscopy, and energy-dispersive X-ray measurements were performed to characterize their structure and composition. In this unique structure, gold nanoparticles were uniformly decorated in the inner wall of Gd0.3Ce0.7O1.9 (GDC) nanotubes with high gold loading. The catalytic activity of a Au-GDC nanotube catalyst for oxygen reduction reaction (ORR) in a 0.1 M KOH solution was studied using a rotating ring-disk electrode (RRDE) technique. RRDE results show that the ORR mainly favors a direct four-electron pathway, and a maximum cathodic limiting current density of -6.70 mA cm(-2) at 2500 rpm was obtained, which is much bigger than that of gold bulk electrode and as-reported gold/rGO hybrid catalysts and close to the behavior of a commercial Pt/C catalyst below -0.8 V. Most importantly, the as-prepared Au-GDC nanotube catalyst exhibits excellent stability for the ORR because of the maximum interaction between gold nanoparticles and GDC nanotube supports.

Phosphorus and cobalt co-doped reduced graphene oxide bifunctional electrocatalyst for oxygen reduction and evolution reactions

Phosphorus (P) and cobalt (Co) co-doped reduced graphene oxide (P-Co-rGO) has been developed and studied through a facile electrostatic assembly followed by a pyrolysis process. The prepared P-Co-rGO catalyst shows a great enhancement in the electrocatalytic activity and stability towards the oxygen reduction reaction (ORR) in alkaline solution, characterized with a positive onset potential of 0.89 V (vs. RHE), a negative shifting of only about 12.8 mV of the half-wave potential and the closest diffusion limiting current density (−5.5 mA cm−2) as compared to those of the commercial Pt/C (20 wt%). More interestingly, the prepared P-Co-rGO also exhibits excellent catalytic activity and stability for the oxygen evolution reaction (OER), with a low potential of 1.62 V (vs. RHE) at the current density of 10 mA cm−2 and a maximum current density of almost 30 mA cm−2 at 1.66 V (vs. RHE). Specifically, the prepared P-Co-rGO shows much higher activity and stability than the mono-doped reduced graphene oxide either with P or Co, respectively. This could be ascribed to the modification of the charge and spin densities and the edge and defect effects of the rGO after the co-doping of P and Co, thus resulting in a remarkable enhancement of the electrocatalytic properties for both the ORR and OER.