Eco-Friendly and Sustainable Production of Bifunctional Carbon Quantum Dots from Pine Cones: Utilizing Dual Fractions and Exploring Polarity-Dependent Electrochemical Properties for Energy Storage Applications

Öz

Carbon quantum dots (CQDs) have gained recognition as promising nanomaterials for energy storage applications, owing to their distinctive attributes including high surface area, tunable surface chemistry, superior electrical conductivity, and cost-effective production from renewable sources. Unlike traditional carbon electrodes which typically operate at only one polarity, an ideal energy storage material should exhibit electrochemical activity across both positive and negative voltage windows to enable high-energy and high-power asymmetric supercapacitors. However, such dual-range functionality remains uncommon in carbonaceous materials. Here, we report a green, one-step hydrothermal synthesis of fluorescent CQDs from Pine cones—an abundant forest waste—and demonstrate, a dual-range electrochemical behavior that, to the best of our knowledge, has rarely been reported for biomass-derived carbons. The CQDs deliver a remarkable specific capacitance of 237 F/g in the positive window (0 to +0.6 V) through mixed pseudocapacitive-EDLC contributions, while simultaneously exhibiting predominantly EDLC behavior with faster ion transport ( apparent D ≈ 10⁻⁷ cm²/s) in the negative window (–0.6 to 0 V). This unexpected polarity-dependent switching of the charge-storage mechanism is attributed to the core–shell architecture of the CQDs: an oxygen-rich shell drives pseudocapacitance under oxidizing conditions, whereas the graphitic sp² core ensures rapid EDLC under reducing potentials. This intrinsic bifunctionality—uncommon in biomass-derived carbons—offers a promising route for designing single-electrode materials capable that operates across the entire voltage spectrum for advanced asymmetric supercapacitors.

Anahtar Kelimeler

• Carbon quantum dots
• hydrothermal carbonization
• Pine Cones
• supercapacitors
• pseudocapacitance
• dual-range electrochemistry

Teşekkür

The author gratefully acknowledges the Central Research Center of Bayburt University for Transmission Electron Microscopy (TEM) analysis, and the KITAM Research Center of Ondokuz Mayıs University for Thermogravimetric Analysis (TGA) and Fourier Transform Infrared (FT-IR) spectroscopy.

Çam kozalaklarından iki fonksiyonlu karbon kuantum noktalarının çevre dostu ve sürdürülebilir üretimi: çift fraksiyonların kullanımı ve enerji depolama uygulamaları için polariteye bağlı elektrokimyasal özelliklerin araştırılması

Öz

Karbon kuantum noktaları (CQDs), yüksek yüzey alanı, ayarlanabilir yüzey kimyası, üstün elektriksel iletkenlik ve yenilenebilir kaynaklardan maliyet etkin üretim gibi kendine özgü özellikleri sayesinde enerji depolama uygulamaları için umut verici nanomalzemeler olarak kabul görmektedir. Genellikle yalnızca tek bir polaritede çalışan geleneksel karbon elektrotların aksine, ideal bir enerji depolama malzemesi, yüksek enerjili ve yüksek güçlü asimetrik süperkapasitörleri mümkün kılmak için hem pozitif hem de negatif voltaj pencerelerinde elektrokimyasal aktivite sergilemelidir. Ancak bu tür çift aralıklı işlevsellik, karbonlu malzemelerde nadir görülen bir durumdur. Bu çalışmada, bol miktarda bulunan bir orman atığı olan çam kozalaklarından yeşil, tek adımlı hidrotermal sentez yoluyla floresan CQDs üretimi raporlanmakta ve biyokütle kaynaklı karbonlar için bildiğimiz kadarıyla nadiren rapor edilmiş çift aralıklı bir elektrokimyasal davranış sergilendiği gösterilmektedir. CQDs, pozitif pencerede (0 ile +0,6 V arası) karışık psödokapasitif-EDLC katkıları aracılığıyla 237 F/g'lik dikkat çekici bir özgül kapasitans değeri sunarken, negatif pencerede (–0,6 ile 0 V arası) aynı anda daha hızlı iyon taşınımı (görünen D ≈ 10⁻⁷ cm²/s) ile birlikte ağırlıklı olarak EDLC davranışı sergilemektedir. Yük depolama mekanizmasındaki bu beklenmedik polariteye bağlı geçiş, CQDs'lerin çekirdek–kabuk mimarisine atfedilmektedir: oksijence zengin kabuk, oksitleyici koşullar altında psödokapasitansı yönlendirirken, grafitik sp² çekirdek indirgeyici potansiyeller altında hızlı EDLC sağlamaktadır. Biyokütle kaynaklı karbonlarda nadir görülen bu içsel çift işlevsellik, tüm voltaj spektrumunda çalışabilen tek elektrotlu malzemelerin tasarımı ve ileri asimetrik süperkapasitörler için umut verici bir yol sunmaktadır.

Anahtar Kelimeler

• Karbon Kuantum Noktalari
• Hidrotermal karbonlasma
• Cam kozalaklari
• Superkapasitorler
• Sahte kapasitans
• Cift aralikli elektrokimya

Teşekkür

Yazar, Geçirimli Elektron Mikroskopi (TEM) analizi için Bayburt Üniversitesi Merkezi Araştırma Merkezi'ne ve Termogravimetrik Analiz (TGA) ve Fourier Dönüşümlü Kızılötesi (FT-IR) spektroskopisi için Ondokuz Mayıs Üniversitesi KITAM Araştırma Merkezi'ne minnettar olduğunu belirtir.

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