DOI: 10.1002/anie.202423092

NH4H2PO4和KH2PO4復合肥料在提高作物產量和品質方面具有顯著優勢。氨（NH?）對于合成這種復合肥是必不可少的，它是通過一個能源密集型的化學過程生產的。開發高效、環保的方法生產含氨復合肥至關重要，而且極具挑戰性。在這里，我們提出了一個串聯催化系統，能夠通過電化學和后續化學過程相結合，在工業規模的反應器中將大量尿素完全轉化為復合肥。在一個典型循環中，使用200 g尿素，無需進一步分離，可產生1580 g固體復合肥（KH2PO4和NH4H2PO4）和232 L純H2。實現該系統的關鍵是精確控制電化學過程中尿素的消耗速率和NO2-的生成速率。通過在電解液中保持尿素與NO2-的精確摩爾濃度比為1/2，尿素可以與NO2-完全反應生成N2，而CNO-可以在H3PO4處理的第二步中轉化為NH4+生成復合肥，實現尿素的完全轉化而不產生副產物。

Figure 1. Comparison of the proposed method and traditional method. (a) Schematic illustration of the traditional method for production of the compound fertilizer.(b) Schematic illustration of the tandem system for production of the compound fertilizer. (c) Comparison of the proposed method and traditional method regardinganticipated market price, H2 generation/consumption, and carbon emissions per ton of compound fertilizer.

Figure 2. Theoretical advantages of the tandem industrial-scale system. (a) A diagram of the relationship between urea, NO2-, CNO- and O2 concentrations andelectrolysis time during one cycle. (b) A simplied diagram illustrating the relationship between the concentration of urea, NO2- and CNO- and the electrolysis timein the electrolytic process. (c) A diagram illustrating the correlation between the residual amount (urea and KNO2), as well as NH4+ levels after acid treatment, inrelation to the concentration ratio of urea to NO2- in the electrolyte.

Figure 3. Implementation of the tandem industrial-scale system. (a) An implementation flowchart. (b) Photographs of the electrolysis unit, reaction unit (acidtreatment unit) and a drying unit within the tandem system. (c) Stability evaluation of the electrochemical process at a constant current density of 200?mA?cm-2 at70?°C. (inset, Photographs of the electrolyte after 50 electrolysis cycles and solid fertilizer in a cycle). (d) Economic profitability diagram. (e) Concentrations ofNO2- and CNO- during UOR as a function of electrolysis time. (f) Concentrations of urea and NH4+ after the tandem system as a function of electrolysis time.

Figure 4. In-depth verification of the tandem industrial-scale system. (a) Concentrations of NO2- and CNO- in the electrolyte solution during UOR (driven by S-NiOOH-Ni(OH)2) as a function of time under the voltage of 0.52 V vs Hg/HgO. (b) Concentrations of NO2- and CNO- in the electrolyte solution during UOR (drivenby NiOOH-Ni(OH)2) as a function of time under the voltage of 0.52 V vs Hg/HgO. (c-d) Concentration of NH4+ and urea in the solution after the urea oxidation andtreatment with H3PO4. (e) XRD patterns of the product (with only KH2PO4 and NH4H2PO4), and KH2PO4 and NH4H2PO4 standard sample. (f) Results of ionchromatography for product with only KH2PO4 and NH4H2PO4 compared with standard anion solutions. (g) I-t curve for 13 cycles. (h) Concentrations of NO2- andCNO- in the electrolyte solution during UOR after 13 cycles.

Figure 5. Active ingredient of typical S-NiOOH-Ni(OH)2 catalyst, UOR performance in a three-electrode cell and DFT computations. (a) TEM image. (b)Synchrotron radiation near side X-ray absorption fine structure (NEXAFS) spectroscopy at the S K-edge for different samples. (c) Normalized Ni K-edgeXANES spectra of Ni foil, Ni(OH)2, NiOOH-Ni(OH)2 and S-NiOOH-Ni(OH)2. (d) In-situ Raman spectra in 1.0 mol L?1 KOH with 0.33 mol L?1 urea solution atvarious potentials for S-NiOOH-Ni(OH)2. (e) Current density of NO2-, N2 and O2 for typical S-NiOOH-Ni(OH)2 at different potential. (f) Current density of NO2-,N2 and O2 for NiOOH-Ni(OH)2 at different potentials. (g) The chemisorption of urea molecule on constructed double-layer catalytic models (S-NiOOH-Ni(OH)2)and the control group (NiOOH-Ni(OH)2), with skeletal formula representing the corresponding intermediate structure. Ordinates represent the Gibbs free energyfor each intermediate under the experimental condition (i.e. urea 0.33 mol·L-1, OH- 1.00 mol·L-1, working voltage -1.28 V versus RHE). The structure charts withblack and green borders respectively represent the IM01 on S-NiOOH-Ni(OH)2 and NiOOH-Ni(OH)2. Legend: silver, Ni; red, O; white, H; blue, N; black, C. Inset,The elementary reaction channel for OER at open circuit potential, with the arrow indicating the elementary reaction requiring the highest working voltage.

我們提出了一種新的解決方案，以現實的工業催化過程為例（陽極電催化尿素氧化與陰極氫氣生產耦合）。提出了一種將電化學過程和后續化學過程相結合的串聯系統，該系統不僅可以消除尿素，還可以生產氫氣和純肥料，實現尿素資源的充分利用。該系統執行工業級工藝（每個循環使用10個電解液），將尿素（或尿素廢水）完全轉化為有價值的化學品（純復合肥料，價格低于當前市場）。在一個典型的循環中，生產1580克復合肥料和232升氫氣，而生產復合肥料的傳統方法需要消耗氫氣。該系統有可能使用部分清潔能源來實現低碳目標。在該體系中，通過一種簡單、易于擴展的方法，開發出了NO2-和CNO-產率高、穩定性好的高性能UOR電催化劑。

NiOOH@Ni(SO4)0.3(OH)1.4（記為S-NiOOH-Ni(OH)2）。首先，通過水熱反應在泡沫鎳上合成了典型的S-NiOOH-Ni(OH)2。通常，2×3 cm2的泡沫Ni在1.0M HNO3溶液、乙醇和去離子水中通過超聲徹底清洗。隨后，將1.16 g六水硝酸鎳和200 mg過硫酸鉀溶解于30 mL去離子水中。將得到的均質溶液轉移到內襯聚四氟乙烯的不銹鋼高壓滅菌器中，將清潔的泡沫Ni（2×3 cm2）浸入其中，在150℃下保持10 h。自然冷卻至室溫后，收集樣品，用乙醇反復洗滌，然后在80℃烘箱中干燥12 h，得到Ni(OH)2@Ni(SO4)0.3(OH)1.4。然后用次氯酸鈉溶液處理樣品，得到最終產物S-NiOOH-Ni(OH)2。在次氯酸鈉溶液中溶解1.6 g氫氧化鈉（有效氯含量6.0%）。隨后，將Ni(OH)2@Ni(SO4)0.3(OH)1.4浸入反應溶液中，在35℃下保持3 h。收集所得產物，用去離子水沖洗多次，在60℃烤箱中干燥24 h，得到最終的S-NiOOH-Ni(OH)2。

NiOOH@Ni(OH)2（記為NiOOH-Ni(OH)2）。通常，將1.5 mmol六水硝酸鎳和2 mmol尿素溶解在30 mL去離子水中。將2×3 cm2的泡沫Ni浸入反應溶液中，將其轉移到50 mL反應釜中，在200℃下保持12 h。冷卻至室溫后，收集樣品，用蒸餾水洗滌數次，在120℃烤箱中干燥24 h，生成Ni(OH)2。然后用次氯酸鈉溶液處理Ni(OH)2，得到最終產物NiOOH-Ni(OH)2。過程類似于NiOOH@Ni(SO4)0.3(OH)1.4。通常將1.6 g氫氧化鈉溶解在次氯酸鈉溶液中（有效氯為6.0%）。將Ni(OH)2片浸入反應溶液中，在35℃下保持3 h，收集產物，用去離子水沖洗數次，在60℃烤箱中干燥24 h，得到NiOOH@Ni(OH)2。

本文實驗中使用的原位紅外電化學ATR系統為合肥原位科技有限公司研發。感謝老師支持和認可！