調節氮化硼材料活性以增強尿素氧化反應的選擇性和反應性—DFT 研究

Abstract

本研究執行於微觀層次上分析氮化硼 (BN) 材料在尿素氧化反應中的吸附行為，並以富含缺陷與金屬摻雜的組織性 BN 線型與粒子型材料為研究對象。我們選用具備較高工程適用性的密度泛函理論 (DFT) 進行系統性先驗分析，並分別估算B12N12、B24N24、平面 h-BN、N 缺陷 h-BN 及鎳摻雜系統的結構穩定性、電子結構、吸附能與反應自由能變化。研究結果顯示，相較於 B12N12 與 B24N24 平面型的h-BN基材經N缺陷修飾後能顯著降低反應步驟的自由能變化，並提升電子傳輸能力與中間體的穩定吸附能力，是提升UOR能效的關鍵修飾策略。尿素分子在此系統中作為反應前驅步驟的關鍵吸附物，其吸附構型與結構合理性對後續反應的自由能具顯著影響。此外，我們亦考察金屬Ni在N缺陷中摻雜的可能性，並分析其對吸附能與UOR反應的正負面影響。儘管Ni可提供穩定且對稱的吸附配位結構，然而其強鍵結特性可能限制中間體的結構重組與質子轉移，使反應電位決定步驟之能障上升，降低整體反應效能。與先前文獻所述Ni-O-Ni結構的選擇性缺陷相符，說明金屬摻雜未必一定能促進催化反應。透過N缺陷工程修飾之平面h-BN在結構可調性、電子活化與反應動力學上皆展現卓越潛力。其具備原料豐富、製程簡易與環保應用潛力，有望應用於未來綠色能源轉換與尿素污染治理，提供新穎且可行之材料設計路徑。This study conducted a microscopic-level analysis of the adsorption behavior of boron nitride (BN) materials in the urea oxidation reaction (UOR), focusing on defect-rich and metal-doped linear and particulate BN materials. Density functional theory (DFT), known for its engineering applicability, was adopted for systematic a priori analysis. Structural stability, electronic structure, adsorption energies, and changes in reaction free energies were calculated for B12N12, B24N24, planar h-BN, nitrogen-defect h-BN, and Ni-doped systems.The results reveal that planar h-BN modified with nitrogen defects demonstrates a significant reduction in the free energy changes during reaction steps and improved electron transport capability and intermediate adsorption stability compared to B12N12 and B24N24. These findings highlight defect engineering as a key strategy for enhancing UOR performance. The urea molecule, as a crucial adsorbate in the pre-reaction stage, exerts a significant influence on the free energy of subsequent reaction steps, depending on its adsorption configuration and structural feasibility.Furthermore, we examined the possibility of Ni doping at nitrogen-defect sites and its dual effects on adsorption energy and UOR activity. Although Ni can offer stable and symmetrical coordination structures for adsorption, its strong bonding may hinder structural rearrangements and proton transfers of intermediates, raising the energy barrier at the rate-determining step and reducing overall catalytic efficiency. This aligns with literature findings that symmetric Ni-O-Ni structures exhibit undesirable selectivity, suggesting that metal doping does not inherently guarantee improved catalytic performance.Planar h-BN modified via nitrogen defect engineering exhibits excellent tunability, electron activation, and reaction kinetics, offering a novel and feasible material design route for future applications in green energy conversion and urea pollution mitigation. With its abundant raw materials, simple synthesis process, and environmental potential, this material system represents a promising direction in electrocatalytic urea oxidation research.