A Wide‐Temperature Adaptive Aqueous Zinc‐Air Battery‐Based on Cu–Co Dual Metal–Nitrogen‐Carbon/Nanoparticle Electrocatalysts

Zinc‐air batteries (ZABs) are promising electrochemical energy storage devices, but the inherent semi‐open configuration and catalytically dependent working principle make their performance vulnerable to temperature. Herein, a tunable multi‐site electrocatalyst is manufactured as the cathode for wide‐temperature adaptive aqueous ZABs, comprising Cu–Co dual metal–nitrogen–carbon‐coupled with metal nanoparticles (CuCo‐NC/NPs). The multi‐components synergistically optimize the electronic structure of active sites in CuCo‐NC/NPs, which endows them with low apparent activation energy (Ea) and high activity for oxygen reduction reaction. Moreover, the CuCo‐NC/NPs‐based aqueous ZABs demonstrate satisfactory stability over 540 h, and a high specific capacity of 806 mAh gzn−1 at 10 mA cm−2 at room temperature, outperforming that of Pt/C and many recent report catalysts based ZABs. Even at −30 and 60 °C, the assembled ZABs can deliver more than 88.1% and 95.5% of its room‐temperature specific capacity, as well as superior cycling stability, paving the way for practical applications of aqueous ZABs under extreme conditions.

theoretical calculations demonstrated that introducing secondary metal-N species into the TM-N-C matrix to form dual metal sites (e.g., Co-Fe, Co-Ni, Mn-Fe)-N-C composites can lead to asymmetric electron distribution around active centers and optimized intermediate adsorption mode, thus lowing E a of ORR/OER and improving the performance of ZABs. [1b,8f,10] In addition, although metal nanoparticles (NPs) are sometimes considered to have insufficient intrinsic electrocatalytic activity and should be avoided in TM-N-C materials, recent works revealed that NPs coated by carbon shells play an important role in tuning the geometric and electronic structure of the active sites. [11] For instance, Sun and coworkers [11a] revealed that FeCo NPs could increase the local charge density of Fe-N moieties, resulting in a reduced O 2 dissociation barrier and enhanced ORR activity. Wang et al. [11b] disclosed that the interaction between Co NPs and Co-N sites can reduce the d-band center of Co atoms and moderate the adsorption/desorption free energy of O-containing intermediates. Moreover, Co NPs could enhance the graphitization degree of the carbon matrix and improve catalyst stability. [11b,12] Therefore, rational coupling of metal NPs and dual metal-N sites on the carbon matrix is expected to be a promising strategy for the cathode in ZABs with high intrinsic activity and high stability, as well as low E a which is capable of mitigating the temperatureinduced fluctuations. However, to the best of our knowledge, constructing tunable dual metal-N-C/NPs hybrids for temperature-tolerant aqueous ZABs has not been realized so far.
Herein, we developed a multi-component catalyst comprising Cu-N x and Co-N x moieties, as well as Co NPs on a nitrogen-doped porous carbon matrix (denoted as CuCo-NC/NPs). Cu atoms not only serve as an electron donor to alter the charge density of Co-N x sites to optimize the adsorption/desorption of intermediates, but also enhance the contents of nitrogen, thus facilitating the ORR process. [13] The Cu 0.5 Co 0.5 -NC/NPs catalyst with low activation energy (E a ) exhibits excellent ORR activity of a high half-wave potential of 0.87 V in 0.1 M KOH, surpassing that of commercial Pt/C. Impressively, The Cu 0.5 Co 0.5 -NC/NPs-based aqueous ZABs exhibit a high peak power density of 170 mW cm À2 , an energy density of 1030 Wh kg Zn

À1
, and a cycling stability over 540 h at room temperature. More importantly, the fabricated ZAB delivers 88.1% and 95.5% of room-temperature specific capacity at À30 and 60°C with superior stability, demonstrating the possibility of practical application in extreme working conditions.

Synthesis and Structural Characterization of the Catalysts
The preparation procedure for CuCo-NC/NPs catalyst is illustrated in Figure S1, Supporting Information. First, CoCuZnbased zeolitic imidazolate frameworks (CoCuZn-ZIFs) were prepared by reacting different molar ratios of Co, Cu, and Zn ions (molar ratio = 0. 2:0.8:9, 0.5:0.5:9 and 0.8:0.2:9) with the dimethylimidazole ligand (named Co 0.2 Cu 0.8 Zn 9 -ZIF, Co 0.5 Cu 0.5 Zn 9 -ZIF, and Co 0.8 Cu 0.2 Zn 9 -ZIF). For comparison, CoZn-ZIF and CuZn-ZIF were prepared through a similar procedure using Co and Zn or Cu and Zn ions as metal sources. Scanning electron microscopy (SEM) images ( Figure S2, Supporting Information) and X-ray diffraction (XRD) patterns ( Figure S3, Supporting Information) reveal that both the CoZn-ZIF, CuZn-ZIF, and CoCuZn-ZIF share similar morphology and crystalline structure. Subsequently, the obtained CoCuZn-ZIFs, CoZn-ZIF, CuZn-ZIF, and ZIF-8 were carbonized under an N 2 atmosphere at 900°C to obtain CuCo-NC/NPs, Co-NC/NPs, Cu-NC, and NC catalysts, respectively. Notably, both the Cu 0.2 Co 0.8 -NC/NPs, Cu 0.5 Co 0.5 -NC/NPs, and Cu 0.8 Co 0.2 -NC/ NPs have particle sizes of about %130 nm (Figure 1a and S4, Supporting Information). The transmission electron microscopy (TEM) image in Figure S5a, Supporting Information, indicates that the Co nanoparticles with a size of %15 nm were embedded in a carbon matrix in Cu 0.5 Co 0.5 -NC/NPs. High-resolution TEM (HRTEM) image in Figure 1b displays two sets of lattice fringes with interplanar spacings of 0.21 and 0.33 nm, corresponding to the (111) plane of Co NPs and the (002) plane of graphite, respectively. The selected area electron diffraction (SAED) pattern ( Figure S5b, Supporting Information) further proves the coexistence of Co NPs and graphite in the Cu 0.5 Co 0.5 -NC/NPs catalyst. Energy dispersive X-ray spectroscopy (EDX) elemental mapping images in Figure 1c and S6, Supporting Information, clearly verify the uniform distribution of Co, Cu, N, and C throughout the whole Cu 0.5 Co 0.5 -NC/NPs catalyst.
The powder X-ray diffraction (XRD) patterns in Figure S7, Supporting Information, show two broad peaks at %24°and 43.6°, corresponding to (002) and (101) planes of graphitic carbon (JCPDS No.41-1487), respectively. Three peaks located at 44.2°, 51.5°, and 75.8°of (111), (200), and (220) assigning to metallic Co . The chemical states of the samples were investigated by X-ray photoelectron spectra (XPS) measurements. Signals for Co, Cu, C, N, and O elements were detected by the XPS survey spectra of Cu 0.5 Co 0.5 -NC/NPs in Figure S8 and Table S1, Supporting Information. Deconvoluted N 1s XPS spectra of Cu 0.5 Co 0.5 -NC/NPs ( Figure 1d) display five peaks around 398.4, 399.2, 400, 401, 401.9 eV, assigning to pyridinic N, M-N, pyrrolic N, graphitic N, and oxidized N. [14] Compared to the Co-NC/NPs, the M-N peak of Cu 0.5 Co 0.5 -NC/NPs shifted to the lower binding energy, meaning that the introduction of Cu could modulate the electron configuration of M-N species, which helps to accelerate the ORR process. [10a] Notably, the N content of Cu 0.5 Co 0.5 -NC/NPs is higher than that of Co-NC/ NPs and Cu-NC (Figure 1e), which may be due to metal has a strong complex ability with N to generate stable M─N bond and preserve a relatively high N content in the carbon framework. [15] It is worth mentioning that the increase of N content is conductive to immobilize the M-N active site resulting in remarkable ORR activity. [13b,16] High-resolution Cu 2p XPS spectra in Figure 1g shows two prominent peaks at 932 and 934.6 eV representing the Cu þ and Cu 2þ species. [17] Noting that the percentage of Cu þ in Cu 0.5 Co 0.5 -NC/NPs is 65%, which is much higher than 39% in Cu-NC ( Figure 1f ). In contrast, Cu in Cu-NC is mainly in the form of Cu 2þ . Previous work demonstrated that the Cu(I)-N species have much higher ORR activity than Cu(II)-N, thus the high activity of Cu 0.5 Co 0.5 -NC/NPs can be expected. [18] Moreover, ultraviolet photoelectron spectrometer (UPS) spectra measurements (Figure 1h) show that the work functions of Cu 0.5 Co 0.5 -NC/NPs and Co-NC/NPs are 4.45 and 4.60 eV, respectively. The lower work function of Cu 0.5 Co 0.5 -NC/NPs indicates its lower energy barrier for electrons transferring from the catalyst surface to oxygen intermediates. [19]

Electrocatalytic Performance of the Catalysts
The ORR performances of as-prepared catalysts were evaluated in O 2 -saturated 0.1 M KOH using a conventional three-electrode system. The CV curves of NC, Cu-NC, Co-NC/NPs, and Cu 0.5 Co 0.5 -NC/NPs ( Figure S9, Supporting Information) show obvious reduction peaks between 0.8 and 0.95 V in O 2 -saturated 0.1 M KOH while those do not appear in Ar-saturated 0.1 M KOH, demonstrating potential ORR activity of these catalysts. The linear sweep voltammetry (LSV) curves in Figure 2a,b displays that the Cu 0.5 Co 0.5 -NC/NPs exhibits excellent ORR activity with high onset potential (E onset = 0.96 V) and half-wave potential (E 1/2 = 0.87 V), which is superior to that of Co-NC/NPs . These results confirm the synergistic effect of Co-N/NPs and Cu-N species on ORR performance. Besides, Cu 0.5 Co 0.5 -NC/NPs catalyst shows faster reaction kinetics of ORR, which owns a small Tafel slope of 53.9 mV dec À1 ( Figure S10, Supporting Information), high kinetic current density ( j k ) of 86.6 mAcm À2 at 0.8 V ( Figure S11, Supporting Information) and low charge transfer resistance ( Figure S12, Supporting Information). Furthermore, the Cu 0.5 Co 0.5 -NC/NPs catalyst possesses a higher double layer capacitance (C dl ) of 19.7mFcm À2 compared with Co-NC/NPs (12.9 mF cm À2 ), demonstrating the increase of surface area and active sites by introducing Cu ( Figure S13, Supporting Information). Rotating ring-disk electrode (RRDE) test was performed to investigate the ORR pathway on the Cu 0.5 Co 0.5 -NC/ NPs. The electron transfer numbers (n) of Cu 0.5 Co 0.5 -NC/NPs catalyst is between 3.85 and 3.93 in the range of 0-0.7 V vs RHE from RRDE results (Figure 2c) and 3.97-4.01 calculated from K-L spots ( Figure S14, Supporting Information), respectively, proving an efficient four-electron ORR process. As shown in Figure 2c and S15, Supporting Information, the Cu 0.5 Co 0.5 -NC/NPs catalyst possesses low ring current and H 2 O 2 selectivity (3-8%), comparable to that of Pt/C (2-5%). It is worth noting that the ORR activity and selectivity of CuCo-NC/NPs can be tuned by varying the atom ratio of Cu and Co ( Figure S16 and Table S2, Supporting Information). Additionally, peroxide reduction reaction (PRR) activity is another crucial parameter to evaluate the performance of ORR catalysts. As shown in Figure S17, Supporting Information, Cu-NC and Cu 0.5 Co 0.5 -NC/NPs have higher PRR activities than NC and Co-NC/NPs, respectively, suggesting that Cu species can accelerate the reduction of hydrogen peroxide, thereby improving the selectivity of 4e À pathway.
To evaluate the intrinsic activity of Cu 0.5 Co 0.5 -NC/NPs, the E a for ORR was determined by the temperature-dependent ORR polarization curves. The LSV curves in Figure S18, Supporting Information, show that the Cu 0.5 Co 0.5 -NC/NPs possess high ORR activity between 10 and 30°C, which exhibits a small performance decline with decreasing temperature. Specifically, the E a of Cu 0.5 Co 0.5 -NC/NPs and Co-NC/NPs catalysts for ORR were calculated at a kinetically controlled region (0.9 V vs RHE) based on the Arrhenius equation. As shown in Figure 2d and Table S3, Supporting Information, the E a of Cu 0.5 Co 0.5 -NC/NPs for ORR is about 13.1 kJ mol À1 , much lower than 22.0 kJ mol À1 of Co-NC/NPs, and comparable to or even surpasses that of other reported electrocatalysts, [20] confirming the high intrinsic ORR activity of Cu 0.5 Co 0.5 -NC/NPs. Stability is another important factor in evaluating catalysts. As illustrated in Figure 2e, the Cu 0.5 Co 0.5 -NC/NPs catalyst has remarkable methanol tolerance with no significant fluctuation after adding 3 M CH 3 OH in 0.1 M KOH, yet the current density of Pt/C drops sharply. Furthermore, chronoamperometric measurement at 0.6 V vs RHE proves that Cu 0.5 Co 0.5 -NC/NPs catalyst exhibits excellent stability with a low attenuation rate of 7% after 20 h operation (Figure 2f ), much better than that of commercial Pt/C (31% loss within less than 6 h). The electrochemical performances of asprepared catalysts for OER were further evaluated in 1 M KOH ( Figure S19, Supporting Information). The Cu 0.5 Co 0.5 -NC/NPs/NF catalyst displays a low polarization overpotential of 380 mV at 10 mA cm À2 , lower than NF (E j = 10 = 470 mV), IrO 2 /NF (E j = 10 = 400 mV), Cu-NC/NF (E j = 10 = 444 mV) and Co-NC/NPs/NF (E j = 10 = 420 mV) catalysts ( Figure S19a, Supporting Information). In addition, the Tafel slope in Figure S19b, Supporting Information, of Cu 0.5 Co 0.5 -NC/NPs/NF catalyst is 64.3 mV dec À1 , which is smaller than NF (83.3 mV dec À1 ), IrO 2 /NF (99.2 mV dec À1 ), Cu-NC/NF (108 mV dec À1 ) and Co-NC/NPs/NF (83.1 mV dec À1 ) catalysts. Consequently, the Cu 0.5 Co 0.5 -NC/NPs catalyst manifests high ORR and OER activity, low H 2 O 2 selectivity, and outstanding durability.

Aqueous ZABs Performance at Room Temperature
Encouraged by the excellent ORR/OER activities of Cu 0.5 Co 0.5 -NC/NPs, a homemade aqueous ZAB was assembled.
Remarkably, the Cu 0.5 Co 0.5 -NC/NPs-based ZAB displays a higher open-circuit voltage of 1.48 V than Pt/C-based ZAB of 1.46 V ( Figure S20, Supporting Information). As shown in Figure 3a,b, the Cu 0.5 Co 0.5 -NC/NPs-based ZAB delivers a peak power density of 170 mW cm À2 at 242 mA cm À2 , a high specific capacity of 806 mAh g zn À1 at a discharge current of 10 mA cm À2 , and an energy density of 1030 Wh kg Zn

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, outperforming Pt/Cbased ZAB (peak power density: 125 mW cm À2 at 145 mA cm À2 ,  ). Impressively, the performance of the Cu 0.5 Co 0.5 -NC/NPs-based ZAB is comparable to or even surpasses that of other reported previously electrocatalysts-based ZABs (Figure 3c and Table S4, Supporting Information). [21] Besides, the ZAB using Cu 0.5 Co 0.5 -NC/NPs as cathode possesses outstanding rate performance ( Figure S21, Supporting Information). The cycling stability of ZAB is tested by galvanostatic charge-discharge cycling technique at 10 mA cm À2 with 20 min for each cycle. The Cu 0.5 Co 0.5 -NC/NPs based ZAB can operate stably over 540 h with a low voltage gap of 0.81 V. Typically, Cu 0.5 Co 0.5 -NC/NPs-based ZAB maintains a voltage gap of 0.78 V at 100 h and 220 h, while it increased from 0.84 V at 100 h to 1.35 V at 220 h for Pt/C þ IrO 2 -based ZAB, implying excellent stability of Cu 0.5 Co 0.5 -NC/NPs-based ZAB (Figure 3d).

Temperature Adaptability of Cu 0.5 Co 0.5 -NC/NPs Based ZAB
To explore the feasibility of Cu 0.5 Co 0.5 -NC/NPs-based ZAB for practical applications in extreme environments (extremely cold/ hot conditions), the battery performance was tested in a wide temperature range from À30 to 60°C (Figure 4a). The Cu 0.5 Co 0.5 -NC/NPs-based ZAB displayed a stable open-circuit voltage of 1.53 V at À30°C ( Figure S22, Supporting Information). When the temperature increased to 60°C, the open-circuit voltage showed a slight decrease to 1.42 V, which may be due to the decrease of oxygen electrode potential and the increase of Zn electrode potential with elevating temperature based on the Nernst equation. The peak power densities of the Cu 0.5 Co 0.5 -NC/NPsbased ZAB are 41. 5, 79.4, 127.5, 215.6, and 267.9 mW cm À2 at temperatures of À30, À20, 0, 40, and 60°C, respectively ( Figure S23, Supporting Information). In addition, the ZAB using Cu 0.5 Co 0.5 ÀNC/NPs as cathode possesses a high capacity of 710, 765, 800, 803, and 770 mAh g Zn À1 at a discharge current density of 10 mA cm À2 and energy density of 844. 9, 933.3, 1010.4, 1035.9, and 1008.7 Wh kg Zn À1 at À30, À20, 0, 40, and 60°C, respectively ( Figure S24, Supporting Information). Impressively, the performance of Cu 0.5 Co 0.5 ÀNC/NPs-based ZAB at À30°C is much higher than that of commercial Pt/C (peak power density of 28.2 mA cm À2 and capacity of 601 mAh g Zn À1 ) ( Figure S25, Supporting Information). Moreover, the Cu 0.5 Co 0.5 ÀNC/NPsbased ZAB affords high capacity retention rates at wide temperatures (À30 to 60°C), which outperforms most of the recently reported ZABs (Figure 4b and Table S5, Supporting Information). [3a,3c,3d,22] The assembled Cu 0.5 Co 0.5 ÀNC/NPs-based ZAB was capable to power LED lamp belt at À30, À20, 0, 25, 40, and 60°C (Figure 4c and S26, Supporting Information). Furthermore, the Cu 0.5 Co 0.5 ÀNC/NPs-based ZAB afford long cycle numbers at wide temperature (À30 to 60°C), which outperforms most of the recently reported ZABs (Figure 4d,e and Table S6, Supporting Information). [3a,3c,3d,22bÀd] Interestingly, the morphology and structure of Cu 0.5 Co 0.5 ÀNC/NPs keep unchanged after 150 h of immersion in 6 M KOH and 0.2 M Zn (CH 3 COO) 2 at 60°C ( Figure S27, Supporting Information). These results reveal that the Cu 0.5 Co 0.5 -NC/NPs-based ZAB possesses satisfactory temperature adaptability, demonstrating the potential for practical applications in extreme conditions.

Conclusion
In summary, a tunable multi-component catalyst was developed for wide-temperature (À30 to 60°C) adaptive ZABs, consisting of Cu-Co dual metal-nitrogen-carbon-coupled with metal Figure 3. Zinc-air batteries (ZABs) performances of Cu 0.5 Co 0.5 -NC/NPs and Pt/C (catalyst loading: 1 mg cm À2 ) at 25°C a) Discharge polarization and power density curves with a scanning rate of 5 mV s À1 . b) Galvanostatic discharge curves from ZABs at 10 mA cm À2 . c) Comparison of the performance of Cu 0.5 Co 0.5 -NC/NPs based ZAB with other reported ZABs. d) Galvanostatic charge-discharge performance of ZABs of Cu 0.5 Co 0.5 -NC/NPs and Pt/C þ IrO 2 at 10 mA cm À2 . nanoparticles (CuCo-NC/NPs). The synergies between Cu-N x , Co-N x moieties, and metal NPs endow the CuCo-NC/NPs composite with optimized active center electronic configuration and work function. Consequently, the Cu 0.5 Co 0.5 -NC/NPs exhibit low apparent activation energy and high activity for ORR with a half-wave potential of 0.87 V. Moreover, the Cu 0.5 Co 0.5 -NC/ NPs-based ZAB exhibits a high peak power density of 170 mW cm À2 , an outstanding specific capacity of 806 mAh g zn À1 , and a superior cycling stability over 540 h at 25°C, outperforming the commercial Pt/C þ IrO 2 couple. Impressively, the fabricated ZABs have excellent temperature adaptability, affording 88.1% and 95.5% of room-temperature specific capacity, as well as superior cycling stability at À30 and 60°C.

Supporting Information
Supporting Information is available from the Wiley Online Library or from the author.