CoNi Nanoalloys @ N-Doped Graphene Encapsulated in N-Doped Carbon Nanotubes for Rechargeable Zn–Air Batteries

Abstract

Exploring cost-effective and durable bifunctional oxygen electrocatalysts for oxygen reduction and oxygen evolution reactions (ORR and OER) is critical for the commercial implementation of rechargeable Zn–air batteries but remains as an immense challenge. Herein, CoNi nanoalloys wrapped with N-doped graphene embedded into N-doped carbon nanotubes (CN@NC) have been prepared by a universal two-step pyrolysis method. The optimal CN@NC–2–800 affords a positive half-wave potential of 0.83 V for ORR and a small overpotential of 400 mV at 10 mA cm–2 for OER, outperforming most of the current non-precious bifunctional oxygen electrocatalysts. Expectedly, the liquid Zn–air battery based on CN@NC–2–800 displays a high open-circuit voltage of 1.52 V, a large peak power density of 172 mW cm–2, and a long cycle life of 300 h. Furthermore, the developed all-solid-state Zn–air battery also shows remarkable stability with various degrees of bending. This work offers a simple and effective way to explore highly efficient and durable electrocatalysts for renewable energy applications.

Large‐Scale Synthesis of FeNi Nanoalloys‐Layered Porous N‐Doped Carbon Nanosheets for Efficient Electrocatalytic Water Splitting

“…In addition, Fe 1 Ni 1 ‐NCS‐900 showed the highest I D /I G of 1.06, indicating that it exhibited sufficient carbon defect sites which was beneficial for the electrochemical activity (Figure 2b) [13] . All of the Fe 1 Ni 1 ‐NCS−T displayed a type IV N 2 adsorption‐desorption isotherm with an obvious hysteresis loop in the relative pressure range of 0.5∼1.0, suggesting the existence of abundant mesopores (Figure 2c, S9) [8a] . The corresponding pore size distribution curves revealed the mesopores mainly centered at 3.7 and 35.3 nm (the inset of Figure 2c, S9), which was consistent with TEM results.…”

“…The presence of N species in carbon substrate can create positive charge sites of nearby carbon species, which is benefit to catalytic activity [4c,13] . In addition, it is generally believed that pyridine N can be used as the active component for electrocatalysis, and metallic N exhibits the most potent metal active sites which also benefits to electrocatalysis [8a,15] . It is worth noting that the pyridine N and metallic N content in Fe 1 Ni 1 ‐NCS‐900 was 25.6% and 7.3%, respectively, which was unambiguously highest, indicating that Fe 1 Ni 1 ‐NCS‐900 may have the best electrocatalytic ability (Figure S12, S13, Table S2).…”

Hierarchical Core–Shell Co2N/CoP Embedded in N, P‐doped Carbon Nanotubes as Efficient Oxygen Reduction Reaction Catalysts for Zn‐air Batteries

“…The observation of subpeaks for both materials at 780.1 eV confirms that Co (III) may combine with N-dopants to form Co−N x species which can generate effective electrocatalytically active sites for ORR. [13,58,61,62] Compared with the peak in accordance with Co−O (781.6 eV) in Co 2 N@NCNTs, the peak corresponding to Co-P (781.5 eV) [55,63] in Co 2 N/CoP@PNCNTs indicates that O coordinating with Co is substituted by P (Figure 2f and Table S3, Supporting Information). Additionally, compared with Co 2 N@NCNTs, the content of N and O decreases and the content of P increases in Co 2 N/CoP@PNCNTs, again confirming that partial N and O are substituted by P (Table S4, Supporting Information).…”

“…The high-resolution N 1s spectra of both Co 2 N@NCNTs and Co 2 N/CoP@PNCNTs (Figure S11b, Supporting Information) display four main peaks: pyridinic-N (398.8 eV), Co-N x (399.4 eV), pyrrolic-N (400.3 eV), and graphitic-N (401.3 eV). [18,36,53,[55][56][57][58] In contrast with other N species, [18] pyridinic N dopant sites are generally accepted as effective catalytic sites for ORR, owing to reducing the energy barrier for adsorption of O 2 on adjacent carbon atoms. [18,59,60] Compared with Co 2 N@NCNTs, the content of pyridinic-N in Co 2 N/CoP@PNCNTs increases from 35.5% to 45.7%, which is favorable for better catalytic efficiency for ORR (Table S2, Supporting Information).…”

Ultrauniformly Dispersed Cu Nanoparticles Embedded in N-Doped Carbon as a Robust Oxygen Electrocatalyst

“…Commercialization of clean and renewable energy conversion technologies, e.g., polymer electrolyte membrane fuel cells (PEMFCs) and metal–air batteries, relies greatly on highly efficient and durable oxygen reduction reaction (ORR) catalysts. − Currently, conventional nanosized platinum-based catalysts are widely used to lower the activation energy of ORR, but their high cost impedes the large-scale commercial application of the renewable energy devices. , Therefore, developing high-efficient and cost-effective nonprecious metal-based catalysts, such as N-doped carbons loaded with transition metals (M/C-N, M = Fe, Co, Cu, etc. ), to replace Pt-based precious metals is essential but still challenging. − …”