成果简介
铜粉作为电子与制造领域不可或缺的基础原材料，面临表面极易快速氧化的固有难题，严重制约其储存、加工与服役稳定性。石墨烯包覆是提升铜粉抗氧化性的有效策略，但常规化学气相沉积（CVD）方法在粉末体系上面临三大瓶颈：高温下颗粒易烧结、前驱体难以高效传输至粉床内部导致覆盖率低、以及单层生长的自限制效应难以实现少层可控沉积。如何突破前驱体在粉末床中的传质受限与颗粒防烧结难题，实现公斤级规模化、高覆盖、少层石墨烯包覆铜粉的可控制备，是推动石墨烯-金属复合材料走向实际应用的关键。本文，北京石墨烯研究院刘忠范院士团队等在《Small》期刊发表名为”Kilogram-Scale Synthesis of Few-Layer Graphene-Skinned Copper Powders via Pulsed-Pressure Chemical Vapor Deposition”的论文，研究提出一种可规模化的脉冲压力CVD（pulsed-pressure CVD）策略，实现了公斤级少层石墨烯包覆铜粉的可控制备。
该策略以石墨粉作为物理隔离剂防止铜颗粒在高温下烧结，通过独特的循环压力调制主动增强前驱体在粉末床内部的渗透与传输，突破常规CVD前驱体传质受限的瓶颈，实现少层石墨烯在铜粉表面的共形包覆。所得铜粉表面形成3-5层、覆盖率高达98.2%且结晶度高的少层石墨烯”皮肤”，展现出优异的抗氧化性能：在190 °C空气中30 min后吸氧量较裸铜粉降低约20倍。由该石墨烯包覆铜粉致密化得到的石墨烯-铜复合材料，热导率较纯铜提升约8%，电导率较纯铜提升约3%。该工作为大规模制备高性能石墨烯-金属复合材料提供了可行路径，为先进导电与热管理应用开辟了新机遇。
图文导读
图1、Pulsed-pressure CVD process for synthesizing few-layer graphene-skinned Cu powders. (a) Schematic diagram of the graphite isolation-assisted pulsed-pressure CVD process. (b,c) Illustration of the few-layer graphene growth facilitated by confined environment (b) and gas flow perturbation (c). (d) SEM image of the graphene-skinned Cu powders. (e–g) Cross-sectional TEM images (e) and SAED characterizations (f,g) of the graphene shell. (h) Raman spectra randomly taken from the as-obtained graphene-skinned Cu powders. (i) Deconvolution of a typical 2D band. (j) Statistical scatter plot of 2D band FWHM versus I2D/IG ratio. (k) Macroscopic view of pristine copper powder and as-obtained graphene-skinned Cu powders.
图2.Selection of graphite isolation agent and its adhesion behavior. (a) Interface formation energy of Cu(111) in contact with graphite(0002), diamond(111), and α-Al2O3(0001) as a function of interfacial separation. (b,c) Differential charge density plots of 3D view along the a-axis (b) and 2D color map (c). (d–f) X-ray nano-CT images of the copper-graphite powder mixture. (g–i) Adhesion behavior of graphite on copper as a function of temperature and time (g), and corresponding SEM images after heat treatment at 1050°C for 10 min (h) and 20 min (i).
图3、Enhanced graphene encapsulation on copper powders via pulsed-pressure CVD. (a) Schematic diagrams comparing the constant-pressure and pulsed-pressure CVD processes. (b) CFD simulations of carbon source concentration distribution at different times. (c,d) Representative SEM images of graphene-encapsulated Cu particles prepared by pulsed-pressure CVD. (e,f) Comparison of the ID/IG ratio from Raman spectra (e) and graphene coverage from SEM images (f) of samples prepared under constant-pressure CVD and pulsed-pressure CVD with varying numbers of pulse cycles.
图4、Oxidation resistance of graphene-skinned Cu powders and enhanced conductivity of their composites. (a) Photographs of bare Cu powder and graphene-skinned Cu powders prepared by constant-pressure and pulsed-pressure CVD, respectively, before and after heating in air at 190°C at various time intervals. (b) Evolution of oxygen content based on semi-quantitative EDS analysis. (c,d) EDS spectra of oxygen signals (c) and XPS spectra of Cu 2p regions (d) after 30 min heating. (e) Thermal conductivity of pure copper and graphene-copper composites measured by laser flash analysis. (f) Electrical conductivity of pure copper and graphene-copper wires with different diameters (Measured by current-bridge method, A: 1.2 mm, B: 0.5 mm, and C: 0.4 mm).
小结
总而言之，本研究提出一种可规模化的脉冲压力CVD策略，以石墨粉为物理隔离剂防止铜颗粒烧结，通过循环压力调制主动增强前驱体在粉末床内部的渗透与传输，实现了公斤级少层石墨烯包覆铜粉的可控制备。所得铜粉表面形成3-5层、覆盖率98.2%且结晶度高的共形石墨烯皮肤，在190 °C空气中30 min后吸氧量较裸铜粉降低约20倍，由其致密化得到的石墨烯-铜复合材料热导率较纯铜提升约8%、电导率较纯铜提升约3%。该工作突破了常规CVD在粉末体系上的烧结-传质-单层自限制三大瓶颈，为大规模制备高性能石墨烯-金属复合材料提供了可行路径，在先进导电与热管理应用领域具有重要应用前景。
文献：https://doi.org/10.1002/smll.74315
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