Manageable N-doped Graphene for High Performance Oxygen Reduction Reaction

Abstract

Catalysts for oxygen reduction reaction (ORR) are at the heart of key green-energy fuel cell technology. N-doped graphene is a potential metal-free electrode with much better electrocatalytic activity, long-term stability, and tolerance to crossover effect than expensive platinum-based electrocatalysts. Here, we report a feasible direct-synthesis method in preparing N-graphene with manageable N contents in a large scale. The resultant N-graphene used as electrocatalysts exhibits similar catalytic activity but superior stability compared to commercial Pt/C for ORR in an alkaline solution. It was found that their electrocatalytic activities were demonstrated to depend largely on N-doping content. When nitrogen content reaches a high value at about 24–25%, ORR reaction exhibits a favorable formation of water via a four-electron pathway. Furthermore, the effect of pyrolysis temperature and precursor on the activity of N-graphene is systematically analyzed, and may shed some light on the principle of choosing appropriate way for preparing N-graphene.

A Library of Doped-Graphene Images via Transmission Electron Microscopy

“…In general, Zhang et al obtained a good result with high N concentrations in two cases of NCU 57 (nitrogen carbon urea) (31.1%), and NCM 57 (nitrogen carbon melamine) (33.7%) regarding the energy dispersed X-ray spectroscopy (EDX) data [88]. As a result, the electrocatalyst for ORR based on NCM 57 -doped graphene showed high catalytic activity, long stability in alkaline atmosphere, and tolerance with a crossover effect [88]. (Figure 10a-f) [96].…”

“…These include (I) gas sensor by B dopant [25], transistor by B dopant [94], N dopant [40,41], NO2 dopant [69]; (II) biosensor by N dopant [86]; (III) solar cell by HNO3 dopant [51,52], SoCl2 dopant [50,51], B dopant [26], HCl dopant [51], H2O2 dopant [51]; (IV) fuel cell by B dopant [27], N dopant [38,96]; (V) Li-ion battery by SnO2/N codopant [35], MoS2/N co-dopant [36], O2 dopant [84]; (VI) supercapacitor by N dopant [39]; (VII) FET by N dopant [44,88], diazonium salt and PEI dopants [74], NH3 dopant [73], N2H4 dopant [61,62], oMeO-DMBI dopant [63]; (VIII) photovoltaic cells by AuCl3 dopant [29]; electrocatalyst for ORR by S/N co-dopant [34], FeN4 dopant [32], N dopant [37,89], P dopant [79,80], N2/P co-dopant [76]; (IX) PLED by TFSA dopant [48]; (X) Free-radical scavenging by P dopant [77]; and (XI) energy storage and conversion by S dopant [33]. In general, the doped-graphene exhibited the diverse potentials with physical and chemical characteristics in further improvement the unexploited and unexplored potential in graphene.…”

“…In general, the doped-graphene exhibited the diverse potentials with physical and chemical characteristics in further improvement the unexploited and unexplored potential in graphene. Plasma doping Ultracapacitor Capacitance (280 F/g), novel cycle life (>200,000), and high-power capability [39] Pyrolysis Catalyst High O-reduction reaction [43] Thermal annealing in APCVD Organic molecular sensing Novel probing of Rhodamine (RhB) molecules [40] Thermal annealing in APCVD Ultrasensitive molecular sensor Novel sensing of RhB, crystal violet (CRV), and methylene blue (MB) molecules [41] Pyrolysis Catalyst High O-reduction reaction [37] Thermal annealing in CVD Fuel cells High O-reduction reactions, long-term stability, tolerance to crossover and poison [38] Plasma doping NA NA [42] Annealing at 1100 • C Back-gate FET Mobility (6000 cm 2 /Vs) [44] Plasma doping Biosensor High electrocatalytic activity, Novel glucose biosensing with low concentration (0.01 mM) [86] Electrothermal annealing FET Highly edge functionalization of GNRs by N 2 species [87] Wet chemical doping Catalyst Good electrocatalytic activity, long term stability, and tolerance to crossover effect [88] Soft thermal doping NA NA [92,94] Solvothermal doping Fuel cell Enhanced catalytic activity in O-reduction reaction [96] Thermal annealing in APCVD NA NA [95] Obviously, the TEM is an important technique to reveal the morphology, crystalline and chemical structures of nanomaterials. The information that TEM techniques can provide and their implications on applications is based on the assistances of low-magnification TEM, HR-TEM, spherical aberration-corrected HR-TEM, BF-TEM, DP-TEM, DF-TEM, STEM, DF-STEM, STEM_EELS, HAADF-STEM, and micro EDS-TEM.…”

“…Similarly, on the same N-doped graphene process, Quan et al also showed the TEM and HR-TEM images of the N-doped graphene (Figure 9j,k) and the pristine solvothermal graphene prepared using N 2 as a precursor (Figure 9l,m) [33]. In 2013, Zhang et al utilized glucose as a reactive carbon source and melamine and urea as N rich molecules for an economical two-step method of N-doped graphene synthesis (Figure 9n-v) [88]. In general, Zhang et al obtained a good result with high N concentrations in two cases of NCU 57 (nitrogen carbon urea) (31.1%), and NCM 57 (nitrogen carbon melamine) (33.7%) regarding the energy dispersed X-ray spectroscopy (EDX) data [88].…”

“…In 2013, Zhang et al utilized glucose as a reactive carbon source and melamine and urea as N rich molecules for an economical two-step method of N-doped graphene synthesis (Figure 9n-v) [88]. In general, Zhang et al obtained a good result with high N concentrations in two cases of NCU 57 (nitrogen carbon urea) (31.1%), and NCM 57 (nitrogen carbon melamine) (33.7%) regarding the energy dispersed X-ray spectroscopy (EDX) data [88]. As a result, the electrocatalyst for ORR based on NCM 57 -doped graphene showed high catalytic activity, long stability in alkaline atmosphere, and tolerance with a crossover effect [88].…”