Evaluation of the stability and durability of Pt and Pt–Co/C catalysts for polymer electrolyte membrane fuel cells

Carbon supported Pt and Pt–Co nanoparticles were prepared by reduction of the metal precursors with NaBH₄. The activity for the oxygen reduction reaction (ORR) of the as-prepared Co-containing catalyst was higher than that of pure Pt. 30 h of constant potential operation at 0.8 V, repetitive potential cycling in the range 0.5–1.0 V and thermal treatments were carried out to evaluate their electrochemical stability. Loss of non-alloyed and, to a less extent, alloyed cobalt was observed after the durability tests with the Pt–Co/C catalyst. The loss in ORR activity following durability tests was higher in Pt–Co/C than in Pt/C, i.e. pure Pt showed higher electrochemical stability than the binary catalyst. The lower stability of the Pt–Co catalyst during repetitive potential cycling was not ascribed to Co loss, but to the dissolution–re-deposition of Pt, forming a surface layer of non-alloyed pure Pt. The lower activity of the Pt–Co catalyst than Pt following the thermal treatment, instead, was due to the presence of non-alloyed Co and its oxides on the catalyst surface, hindering the molecular oxygen to reach the Pt sites.     

Improvement of methanol electro-oxidation activity of PtRu/C and PtNiCr/C catalysts by anodic treatment

The effect of an anodic treatment on the methanol oxidation activity of PtRu/C (50:50 at.%) and PtNiCr/C (Pt:Ni:Cr = 28:36:36 at.%) catalysts was investigated for various potential limits of 0.9, 1.1, 1.3 and 1.4 V (vs. reference hydrogen electrode, RHE). NaBH₄ reduced catalysts were further reduced at 900 °C for 5 min in an argon balanced hydrogen flow stream. Improved alloying was obtained by the hydrogen reduction procedure as confirmed by X-ray diffraction results. In the PtRu/C catalyst, a decrease of irreversible Ru (hydrous) oxide formation was observed when the anodic treatment was performed at 1.1 V (vs. RHE) or higher potentials. In chronoamperometry testing performed for 60 min at 0.6 V (vs. RHE), the highest activity of the PtRu/C catalyst was observed when anodic treatment was performed at 1.3 V (vs. RHE). The current density increased from 1.71 to 4.06 A g_cat.⁻¹ after the anodic treatment. In the PtNiCr/C catalyst, dissolution of Ni and Cr was observed when potentials ≥1.3 V (vs. RHE) were applied during the anodic treatment. In MOR activity tests, the current density of the PtNiCr/C catalyst dramatically increased by more than 13.5 times (from 0.182 to 2.47 A g_cat.⁻¹) when an anodic treatment was performed at 1.4 V. On an A g_{noble metal}⁻¹ basis, the current density of PtNiCr-1.4V is slightly higher than the best anodically treated PtRu-1.3V catalyst, suggesting the PtNiCr catalyst is a promising candidate to replace the PtRu catalysts.     

Melamine-assisted synthesis of paper mill sludge-based carbon nanotube/nanoporous carbon nanocomposite for enhanced electrocatalytic oxygen reduction activity

Developing efficient and cheap electrocatalysts as substitutes for commercial Pt/C in the oxygen reduction reaction(ORR)is extremely necessary. Herein, paper mill sludge (PMS) was utilized to produce iron, nitrogen and sulfur co-doped carbon nanotube/nanoporous carbon nanocomposite (PMS-CNT/C) by pyrolysis. PMS-CNT/C-b, one of as-prepared PMS-CNT/C exhibited excellent oxygen reduction reaction activity with an onset potential of 0.99 V vs. RHE and half-wave potential of 0.77 V vs. RHE, which was similar to the commercial Pt/C catalyst (onset potential of 0.99 V vs. RHE and half-wave potential of 0.76 V vs. RHE). It had longer-term stability and higher methanol tolerance in alkaline medium than Pt/C. Moreover, the new catalyst also exhibited excellent catalytic performance in neutral solution. The energy output of microbial fuel cells loaded with PMS-CNT/C-b catalyst was also higher than that of commercial Pt/C under neutral condition. The excellent ORR performance of PMS-CNT/C-b was due to the carbon nanotube/nanoporous structure and the synergistic effect of abundant N groups, iron nitrides and thiophene-S. The formation of CNTs in the carbon nanotube/nanoporous carbon nanocomposite was mainly attributed to melamine, which was added into PMS and was at first just considered as a nitrogen source to develop N-doped PMS-based catalysis in this work. The synthesis of paper mill sludge-based carbon nanotube/nanoporous nanocomposite and its excellent ORR activity will make the new catalyst a promising cathodic electrocatalyst alternative for fuel cells.     

Investigation of Pt/WC/C catalyst for methanol electro-oxidation and oxygen electro-reduction

A Pt/WC/C catalyst is developed to increase the methanol electro-oxidation (MOR) and oxygen electro-reduction (ORR) activities of the Pt/C catalyst. Cyclic voltammetry and CO stripping results show that spill-over of H⁺ occurs in Pt/WC/C, and this is confirmed by comparing the desorption area values for H⁺ and CO. A significant reduction in the potential of the CO electro-oxidation peak from 0.81 V for Pt/C to 0.68 V for Pt/WC/C is observed in CO stripping test results. This indicates that an increase in the activity for CO electro-oxidation is achieved by replacing the carbon support with WC. Preferential deposition of Pt on WC rather than on the carbon support is investigated by complementary analysis of CO stripping, transmission electron microscopy and concentration mapping by energy dispersive spectroscopy. The Pt/WC/C catalyst exhibits a specific activity of 170 mA m⁻² for MOR. This is 42% higher than that for the Pt/C catalyst, viz., 120 mA m⁻². The Pt/WC/C catalyst also exhibits a much higher current density for ORR, i.e., 0.87 mA cm⁻² compared with 0.36 mA cm⁻² for Pt/C at 0.7 V. In the presence of methanol, the Pt/WC/C catalyst still maintains a higher current density than the Pt/C catalyst.     

H2-induced thermal treatment significantly influences the development of a high performance low-platinum core-shell PtNi/C alloyed oxygen reduction catalyst

In the purpose of maximizing the utilization of noble metal Pt in oxygen reduction catalysts, we illustrate a synthesis method of preparing the low-platinum PtNi/C alloyed oxygen reduction reaction (ORR) catalyst, which is developed through the H₂-induced treatment to a glucose reduced PtNi/C alloy. After post-treatment with H₂/N₂ mixture gases, this catalyst displays excellent ORR catalytic activity and durability for the synergetic influences of electronic and geometry effects on catalysts during the alloying. Specifically, the as-prepared PtNi/C (350°C-6 h) sample delivers preponderant ORR activity with only 53.5% Pt usage than the commercial Pt/C. The specific activity and mass activity are corresponding 7.49 times and 3.5 times to the commercial Pt/C. This catalyst exhibits excellent ORR catalytic activity after 10 000 potential cycles in acid, which benefits from the well alloyed core-shell structure of PtNi/C. H₂-induced thermal treatment has significant effects on the development of high performance low-platinum PtNi/C alloy catalyst, and plays the significant role in the formation of well-alloyed core-shell structures. The lowered d-band center is believed to facilitate ORR catalysis through weakening the adsorption of intermediate oxygen species on the alloyed Pt surface. Therefore, PtNi/C(350°C-6 h) alloyed catalyst possesses outstanding ORR catalytic activity with much lower Pt loading.     

High surface area synthesis,electrochemical activity,and stability of tungsten carbide supported Pt during oxygen reduction in proton exchange membrane fuel cells

The oxidation of carbon catalyst supports to carbon dioxide gas leads to degradation in catalyst performance over time in proton exchange membrane fuel cells (PEMFCs). The electrochemical stability of Pt supported on tungsten carbide has been evaluated on a carbon-based gas diffusion layer (GDL) at 80 °C and compared to that of HiSpec 4000™ Pt/Vulcan XC-72R in 0.5 M H₂SO₄. Due to other electrochemical processes occurring on the GDL, detailed studies were also performed on a gold mesh substrate. The oxygen reduction reaction (ORR) activity was measured both before and after accelerated oxidation cycles between +0.6 V and +1.8 V vs. RHE. Tafel plots show that the ORR activity remained high even after accelerated oxidation tests for Pt/tungsten carbide, while the ORR activity was extremely poor after accelerated oxidation tests for HiSpec 4000™. In order to make high surface area tungsten carbide, three synthesis routes were investigated. Magnetron sputtering of tungsten on carbon was found to be the most promising route, but needs further optimization.     

Effect of Ti addition to Pt/C catalyst on methanol electro-oxidation and oxygen electro-reduction reactions

Carbon supported binary Pt-Ti alloys were investigated for application in methanol electro-oxidation (MOR) and oxygen electro-reduction reactions (ORR). Various compositions of Pt_100−xTi_x/C (x = 0, 25, 50, and 75) catalysts were synthesized by sequential impregnation of Pt and Ti followed by annealing at 900 °C for 30 min under H₂/Ar flow. X-ray diffraction results showed formation of the Pt₃Ti intermetallic phase in Pt₅₀Ti₅₀ and Pt₂₅Ti₇₅ catalysts after annealing at 900 °C. The Pt₅₀Ti₅₀/C-900 and Pt₂₅Ti₇₅/C-900 catalysts (the ‘-900’ designation indicates the catalyst was annealed at 900 °C) exhibited 103% () and 198% () higher MOR activity, respectively, than in the Pt/C-900 catalyst () at 0.7 V (vs. reversible hydrogen electrode (RHE)). These two catalysts also showed high ORR activity. From a specific activity basis, the Pt₅₀Ti₅₀/C-900 and Pt₂₅Ti₇₅/C-900 catalysts exhibited , respectively, which were 171 and 154% higher than the value of the Pt/C catalyst at 0.8 V (vs. RHE). Methanol-tolerant ORR activity was also investigated, but in the presence of methanol, the Pt₅₀Ti₅₀/C-900 and Pt₂₅Ti₇₅/C-900 catalysts both exhibited poor ORR activity.     

Carbon supported Pt–Co (3:1) alloy as improved cathode electrocatalyst for direct ethanol fuel cells

In direct alcohol fuel cells, ethanol crossover causes a less serious effect compared to that of methanol because of both its smaller permeability through the Nafion^® membrane and its slower electrochemical oxidation kinetics on a Pt/C cathode. The main interest in direct ethanol fuel cells (DEFCs) is to find an anode catalyst with high activity for the oxidation of ethanol. However, due to the low activity of pure platinum for the oxygen reduction reaction (ORR), research on cathode electrocatalysts with improved ORR and the same or improved ethanol tolerance than that of Pt are also in progress. In this work, a commercial carbon supported Pt–Co (3:1) electrocatalyst (E-TEK) was investigated as cathode material in DEFCs and the activity compared to that of Pt. In the cathodic potential region (0.7–0.9 V versus RHE) Pt/C and Pt–Co/C showed the same activity for the oxidation of crossover ethanol. But the performance of Pt–Co/C as cathode material in DEFCs in the temperature range 60–100 °C is better than that of Pt/C both in terms of mass activity and specific activity, due to an improved activity of the alloy for oxygen reduction.     

Platinum/tin oxide/carbon cathode catalyst for high temperature PEM fuel cell

The performance of high temperature polymer electrolyte fuel cell (HT-PEMFC) using platinum supported over tin oxide and Vulcan carbon (Pt/SnOx/C) as cathode catalyst was evaluated at 160-200 °C and compared with Pt/C. This paper reports first time the Pt/SnOx/C preparation, fuel cell performance, and durability test up to 200 h. Pt/SnOx/C of varying SnO compositions were characterized using XRD, SEM, TEM, EDX and EIS. The face-centered cubic structure of nanosized Pt becomes evident from XRD data. TEM and EDX measurements established that the average size of the Pt nanoparticles were ∼6 nm. Low ionic resistances were derived from EIS, which ranged from 0.5 to 5 Ω-cm² for cathode and 0.05 to 0.1 Ω-cm² for phosphoric acid, doped PBI membrane. The addition of the SnOx to Pt/C significantly promoted the catalytic activity for the oxygen reduction reaction (ORR). The 7 wt.% SnO in Pt/SnO₂/C catalyst showed the highest electro-oxidation activity for ORR. High temperature PEMFC measurements performed at 180 °C under dry gases (H₂ and O₂) showed 0.58 V at a current density of 200 mA cm⁻², while only 0.40 V was obtained in the case of Pt/C catalyst. When the catalyst contained higher concentrations of tin oxide, the performance decreased as a result of mass transport limitations within the electrode. Durability tests showed that Pt/SnOx/C catalysts prepared in this work were stable under fuel cell working conditions, during 200 h at 180 °C demonstrate as potential cathode catalyst for HT-PEMFCs.     

An efficient Co-N/C electrocatalyst for oxygen reduction facilely prepared by tuning cobalt species content

Transition metal and nitrogen co-doped carbon catalysts for the oxygen reduction reaction (ORR) have emerged as promising candidates to replace the expensive platinum catalysts but still remain a great challenge. Herein, a novel and efficient nitrogen-doped carbon material with metal cobalt co-dopant (Co–N/C) has been prepared by pyrolyzing porphyrin-based covalent organic polymer where Co is anchored. The optimized 10%-Co-N/C catalyst through facilely and efficiently tuning the cobalt content is carefully characterized by XRD, Raman, XPS, SEM and TEM for composition and microstructure analysis. This catalyst with only 0.56% Co exhibits an excellent ORR catalytic activity with a positive half-wave potential of 0.816 V (vs. RHE) in 0.1 M KOH solution, which is comparable to that of commercial Pt/C (20 wt%). Notably, the 10%-Co-N/C catalyst displays better electrochemical stability with only a loss of 5.1% of its initial current density in chronoamperometric measurement and also gives rise to stronger methanol tolerance than Pt/C. The good ORR catalytic behaviour for this catalyst may be attributed to the dispersion of the Co-N_X active sites via adjusting the contents of cobalt species in porous organic framework.     

Efficient oxygen reduction electrocatalysis on Mn3O4 nanoparticles decorated N-doped carbon with hierarchical porosity and abundant active sites

Transition metal on nitrogen-doped carbons (M-N-C, M = Fe, Co, Mn, etc.) are a group of promising sustainable electrocatalysts toward oxygen reduction reaction (ORR). Compared to its Fe, Co analogues, Mn–N–C possesses the advantage of being inert for catalyzing Fenton reaction, and thus is expected to offer higher durability, but its ORR activity needs essential improvement. Herein, an efficient Mn–N–C ORR catalyst composed of Mn₃O₄ nanoparticles supported on nitrogen-doped carbon was successfully synthesized by pyrolysis of cyanamide/Mn-incorporated polydopamine (PDA) film coated carbon black (CB), where the presence of N-rich cyanamide confers abundant Mn-N_x active sites and rich micropore/mesopores to the catalyst. In an alkaline medium, as-synthesized Mn–N–C electrocatalyst outperforms commercial Pt/C catalyst in terms of onset potential (0.98 V, vs. RHE), half-wave potential (0.868 V, vs. RHE), and limiting current density. Meanwhile, it exhibits excellent durability and resistance to methanol. In a Zinc-air primary battery, it demonstrates better performance as a cathodic catalyst than Pt/C.     

Polyoxomolybdate anchored graphite oxide: Noble metal-free electrocatalyst for oxygen reduction reaction

We present the synthesis of a noble metal-free electrocatalyst, polyoxomolybdate/reduced graphite oxide (PMA/rGO) composite, which showed enhancement in the kinetics for oxygen reduction reaction (ORR). The composite material was prepared by simple and cost effective method. Mere heating of the precursors at low temperature (200 °C) resulted in molecular assembly of PMA on GO in the form of clusters which behaved as active centers for efficient ORR. The electrochemical study of PMA/rGO-2 (PMA to GO weight ratio of 1:2) catalyst carried out by rotating disk electrode (RDE) method, showed considerable electrocatalytic activity with E_onset of 1.0 V vs. RHE and current density of 4.0 mA/cm² at 1600 rpm in alkaline condition. Additionally, as-prepared PMA/rGO-2 catalyst showed a single step ~ 4 electron transfer pathway similar to commercial Pt/C catalyst; confirmed through rotating ring disk electrode (RRDE) study. Interestingly, PMA/rGO-2 electrocatalyst exhibited substantially higher stability than Pt/C catalyst even after 20K potential cycles (though the current density of former catalyst is inferior to later). Further, in a methanol cross-over test, PMA/rGO-2 was found to be inactive towards methanol oxidation reactions, which could nullify the issues due to the fuel cross-over effect, if employed as cathode in direct methanol fuel cells. The enhanced ORR activity and significant stability is attributable to the anchoring and homogenous distribution of polyoxomolybdate clusters on graphite oxide.     

Natural aloe vera derived Pt supported N-doped porous carbon: A highly durable cathode catalyst of PEM fuel cell

Evolution of highly durable electrocatalyst for oxygen reduction reaction (ORR) is the most critical barrier in commercializing polymer electrolyte membrane fuel cell (PEMFC). In this work, Pt deposited N-doped mesoporous carbon derived from Aloe Vera is developed as an efficient and robust electro catalyst for ORR. Due to its high mesoporous nature, the aloe vera derived carbon (AVC) play a very vital role in supporting Pt nanoparticles (NPs) with N-doping. After doping N into AVC, more defects are created which facilitates uniform distribution of Pt NPs leading to more active sites towards ORR. Pt/N-AVC shows excellent ORR activity when compared with commercial Pt/C and showing a half wave potential (E_1/2–0.87 V Vs. RHE) and reduction potential (E_red ~ 0.72 V Vs. RHE) towards ORR. Even after 30,000 potential cycles, Pt/N-AVC shows in its E_1/2 only ~5 mV negative shift and lesser agglomeration of Pt NPs is seen in the catalyst. In membrane electrode assembly (MEA) fabrication, Pt/N-AVC as a cathode catalyst in a PEMFC fixture and performance were studied. The Pt/N-AVC shows good performance, which proves the potential application of this naturally available bio derived carbon, which serves as an excellent high durable support material in PEMFC. All these features show that the Pt/N-AVC is the most stable, efficient and suitable candidate for ORR catalyst.     

Rationale approach of nitrogen doping at defect sites of multiwalled carbon nanotubes: A strategy for oxygen reduction electrocatalysis

A development of electrocatalyst for oxygen reduction reaction (ORR) is one of the crucial reactions for low temperature fuel cell applications. The state-of-the-art catalyst (platinum based) have various limitations such as low abundance, extortionate price and sensitive towards impurities. Therefore, design of high performance non-platinum electrocatalyst is the most challenging issue for low temperature fuel cell. In this work, we discuss the nitrogen doping at defect sites of multiwalled carbon nanotubes (MWCNTs) using melamine foam as a template for efficient CNT assembly with subsequent role of different nitrogen containing agents such as melamine and hexamine. Templated assembly of functionalized CNT through melamine foam provides easy approach towards nitrogen doping that followed effective exposure of active sites (like pyridinic-N and oxidic-N) for electroreduction of oxygen. As-prepared N-CNT catalysts (prepared using both the precursors) show better ORR activity than Pt/C in alkaline medium. A sharp reduction peak in their cyclic voltammogram under O₂-saturated 0.1 M KOH solution proves their activity towards ORR electrocatalysis. More interestingly, the onset potentials of ~0.92 V and ~1.1 V versus RHE for N-CNT obtained by hexamine and melamine respectively indicate superior onsets than that of Pt/C (~1.04 V vs RHE). Furthermore, the best N-CNT catalyst (obtained by melamine) reveals better stability up to 15,000 cycles than Pt/C with zero response towards methanol, exhibiting an excellent methanol tolerance.     

Low Pt-loading Ni-Pt and Pt deposits on Ni: Preparation, activity and investigation of electronic properties

A unique, self-limiting, galvanostatic deposition was used to synthesize co-deposits of Ni and Pt onto nickel substrates from sonicated solutions of 0.2 M NiCl₂ in 2.0 M NH₄Cl, with a platinum blacked counter electrode as the sole platinum source. Depositions of only Pt onto the nickel substrates were also performed using this method. Cyclic voltammetry, chronoamperometry, carbon monoxide stripping voltammetry, inductively coupled plasma mass spectrometry, scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy were performed on the deposits. Results demonstrate that, due to the self-regulating nature of this deposition, the Pt-content of the co-deposits does not exceed 8 mol% loading and most of the Pt resides at or near the catalyst surface. The surface atom normalized activities of the co-deposits (Ni-Pt on Ni foam) and Pt-only deposits (Pt on Ni foam) were up to 37 times higher than platinum black towards 2-propanol electro-oxidation in base at 500 mV vs. RHE; the order of activity is Pt on Ni foam ? Ni-Pt on Ni foam > Pt black. The Ni-Pt and Pt on Ni foam catalysts are more active than Pt black at >500 mV mainly via the bi-functional mechanism and some electronic effects. The Pt on Ni foam was the most superior catalyst due to a combination of geometric and bi-functional effects.     

Molecule-confined modification of graphitic C3N4 to design mesopore-dominated Fe-N-C hybrid electrocatalyst for oxygen reduction reaction

To design inexpensive carbon catalysts and enhance their oxygen reduction reaction (ORR) activity is critical for developing efficient energy-conversion systems. In this work, a novel Fe-N-C hybrid electrocatalyst with carbon nanolayers-encapsulated Fe₃O₄ nanoparticles is synthesized successfully by utilizing the molecular-level confinement of graphitic C₃N₄ structures via hemin biomaterial. Benefiting from the Fe-N structure prevalent on the carbon nanosheets and large mesopore-dominated specific surface area, the synthesized catalyst under optimized conditions shows excellent electrocatalytic performance for ORR with an E_ORR at 1.08 V versus reversible hydrogen electrode (RHE) and an E_1/2 at 0.87 V vs. RHE, and outstanding long-term stability, which is superior to commercial Pt/C catalysts (E_ORR at 1.04 V versus RHE and E_1/2 at 0.84 V versus RHE). Moreover, the low hydrogen peroxide yield (<11%) and average electron transfer number (~3.8) indicate a four-electron ORR pathway. Besides, the maximum power density of the home-made Zn-air battery using the obtained catalyst is 97.6 mW cm⁻². This work provides a practical route for the synthesis of cheap and efficient ORR electrocatalysts in metal-air battery systems.     

Effect of thermal annealing on the properties of Corich core–Ptrich shell/C oxygen reduction electrocatalyst

The properties and the oxygen reduction reaction (ORR) characteristics of Pt/C and Co_{rich core}–Pt_{rich shell}/C, which were prepared by the thermal decomposition and the chemical reduction methods, annealed in the various conditions were investigated. The alloying degree and grain size of Co_{rich core}–Pt_{rich shell}/C analyzed by XRD was increased from 13.10% and 2.45 nm to 42.83% and 2.62 nm by increasing the time for annealing at 400 °C in N₂ (annealing condition 1) from 0 to 15 h. When the Co_{rich core}–Pt_{rich shell}/C was annealed in air at 250 °C and then reduced in 6% H₂ at 400 °C (annealing condition 2), the alloying degree and grain size were obtained to be 47.26% and 3.79 nm, respectively. The decrease in the atomic ratio of Co/Pt from 4.77 to 1.34 by annealing Co_{rich core}–Pt_{rich shell}/C in condition 1 from 0 to 15 h was deduced to be the increase in the Pt loading by the reduction of residual Pt precursor to Pt. The mass and specific activities (MA, SA) of the ORR at 0.9 V (versus RHE) on Pt/C annealed in condition 2 were obtained to be 4.11 A g⁻¹ and 6.12 μA cm⁻², respectively. The MA and SA of Co_{rich core}–Pt_{rich shell}/C annealed by condition 2 were 10.07 A g⁻¹ and 11.27 μA cm⁻².     

Methanol tolerant core-shell RuFeSe@Pt/C catalyst for oxygen reduction reaction

Pt decorated RuFeSe/C catalyst is prepared by reduction of Pt precursor on pre-formed RuFeSe/C for oxygen reduction reaction (ORR). The catalyst is characterized by X-ray diffraction (XRD), energy dispersive spectrometer (EDS), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The catalyst particles are found to disperse on the carbon support with an average particle size of 2.8 nm. Physical characterizations and electrochemical tests confirm that Pt is deposited on the surfaces of RuFeSe particles and RuFeSe@Pt/C catalyst has a core-shell structure. The as-prepared catalyst has high durability and shows high ORR activity through a four-electron transfer process. RuFeSe@Pt/C exhibits 1.3-fold greater specific activity and 1.4-fold greater mass activity for ORR than Pt/C. More importantly, it has excellent tolerance to methanol. Consequently, RuFeSe@Pt/C may be used as fine cathode catalyst in direct methanol fuel cells (DMFCs).     

Spinel oxides wrapped on electrospun carbon nanofibers: Superior electrocatalysts boosted by enhanced conductivity and rich oxygen vacancies

Spinel oxides have been considered as promising precious metal-free catalysts for oxygen reduction reaction (ORR). However, the poor intrinsic conductivity and moderate electrocatalytic performance hinder their practical applications. Hence, various strategies have been explored and reported in addressing the issues. Herein, an elaborate approach for enhancing the ORR performance of spinel NiCo₂O₄ is proposed, by combining the decoration of NiCo₂O₄ nanoparticles on electrospun carbon nanofibers and defect engineering with rich oxygen vacancies on NiCo₂O₄ nanoparticles through a facilely controlling on calcination circumstance, which could not only increase more active sites and improve the intrinsic catalytic activity, but also render an excellent stability for long-term operation. Thus, the as-prepared hybrid exhibits significantly improved ORR electrocatalytic performance, including a high limited current density of −5.8 mA cm⁻², a positively shifting of the onset potential at 0.88 V and half-wave potential at 0.76 V (vs. RHE). The performance of rechargeable Zn-air battery based on the as-prepared catalyst surpasses the one based on Pt/C catalyst significantly. This work can be also applied to other metal oxides based electrocatalysts, and then provided an avenue for the realization of metal-air batteries and fuel cells with high efficient and cost-effective.