Angew. Chem. ：生物质到甲酸的高效催化转化耦合低能耗电解水制氢

电解水制氢是未来大规模工业制氢的理想选择之一。其中，质子交换膜电解水技术（PEM）与光伏、风电等可再生能源具有更好匹配性，成为当前电解水制氢的一个重点发展方向。不利因素是酸性电解质中电解水析氧半反应（OER）的动力学非常缓慢，占用大量能耗。解决上述问题的可行策略之一是寻找酸性介质下可替代OER且具有高附加值的催化氧化反应，并耦合电解水制氢构建全新的低能耗电解反应系统。尽管该策略在碱性介质中有研究报道，但在酸性介质中的替代反应尚未被开拓。近日，东北师范大学李阳光教授，谭华桥教授与中南大学刘伟教授合作，开发了一种基于多酸的电催化生物质氧化高效制备甲酸的反应，可用于耦合构建低能耗电解水制氢系统。

Figure 1 (a) Schematic diagram of conventional PEM water electrolysis; (b) Industrial methods for the synthesis of FA; (c) Schematic illustration of the co-production system of FA and hydrogen.

在该系统中，以多金属氧酸盐（POMs）作为阳极氧化还原电解质，在90 ℃将葡萄糖等糖类底物氧化成甲酸，同时在阴极连续电解水制氢。当以H₆[PMo₉V₃O₄₀]作为阳极电解质时，葡萄糖到甲酸的产率高达62.5 %，且甲酸是唯一的液相产物。作者也对不同糖类底物的适用性进行了考察，结果表明：果糖、蔗糖、淀粉、纤维素和秸秆等都能较好地转化为甲酸，且该体系在充足葡萄糖存在的条件下，可连续稳定运行超过100 小时。

Figure 2 (a) The effects of POM species on the conversion of glucose and the yield of FA. Reaction conditions: voltage: 1.0 V (vs. Ag/AgCl), the concentration of various POMs: 0.3 M, the concentration of glucose: 0.1 M, temperature: 90 °C, reaction time: 8 h; (b) The effects of temperature on the conversion of glucose and the yield of FA. Reaction conditions: voltage: 1.0 V (vs. Ag/AgCl), the concentration of H₆[PMo₉V₃O₄₀]: 0.3 M, the concentration of glucose: 0.1 M, reaction time: 8 h; (c) Effects of different voltage on the conversion of glucose and yield of FA. Reaction conditions: the concentration of H₆[PMo₉V₃O₄₀]: 0.3 M, the concentration of glucose: 0.1 M, temperature: 90 °C, reaction time:8 h; (d) The glucose conversion and FA yield of H₆[PMo₉V₃O₄₀] recycled for five times; (e) The conversion and FA yield of different substrates. Reaction conditions: voltage: 1.0 V (vs. Ag/AgCl), the concentration of H6[PV3Mo9O40]: 0.3 M, the concentration of various substrates: 0.1 M, temperature: 90 °C, reaction time: 8 h; (f) Comparison of this work with the reported on the yield of FA, reaction temperature and pressure. Error bars represent the s.d. of at least three independent measurements.

机理研究表明，多酸在热催化的条件下将葡萄糖氧化生成甲酸，同时自身被还原为杂多蓝（还原态多酸简称HPB）。随后，杂多蓝再进一步被阳极电化学氧化，进而实现催化循环。值得一提的是，由于多酸与葡萄糖在均相电解液中反应，且其杂多蓝氧化电位较OER电位显著降低，因此导致该体系摆脱了复杂的电极设计和电极反应，电解水制氢能耗大幅降低。

Figure 3. Schematic diagram of the redox cycle in the anode chamber.

该耦合系统仅需1.22 V即可达到50 mA/cm² 的电流密度，其析氢法拉第效率接近100 %，产氢能耗仅需2.9 kw·h·Nm^-3 (H₂)，仅为传统电解水制氢能耗（4.2 kw·h·Nm^-3 (H₂)）的69 %，展现出超低的能耗。此外，该系统还可以直接由太阳能电池驱动，其经济效益约为传统电解水制氢的5.4倍。

Figure 4 (a) The LSV curves of anode in the mixture of 3 M glucose and 0.3 M H₆[PMo₉V₃O₄₀] electrolyte after 3 h pre-reaction and 1 M H₃PO₄ electrolyte at 90 °C; (b) The power consumption analysis of this system. (c) Comparison of this work with the voltage required for electrocatalytic biomass conversion coupled with hydrogen production systems reported in the literature [22]; (d) Measured H₂ quantity compared with theoretically calculated H₂ quantity assuming a 100% Faradaic efficiency for the H₂ evolution. Theoretical H₂ = (total charge during potentiostatic electrolysis) × 2/ F, where F is the Faraday constant (96485 C mol⁻¹); (e) Economic efficiency analysis of conventional hydrogen production and the present work. The economic benefits of the whole system were calculated according to the price of hydrogen 2.5 $/kg, oxygen 0.108 $/kg, and FA 0.975 $/kg. Taking the power consumption of 1000 kWh as an example, the traditional electrolysis water hydrogen production device can produce about 21.2 kg H₂, which is worth 53.0 $, and the anode can produce about 169 kg O₂, which is worth 18.3$. The total economic value is 71.3 $. If we input a voltage of 1.22 V, we will get 30.7 kg of H₂, worth 76.7 $. In the anode electrolyte, approximately 321.0 kg of primary FA will be produced. Assuming that FA is obtained by distillation, it will consume approximately 45 kWh of electricity (0.11 $/kWh). Its value is about 308.0 $. The total value will reach 384.7 $, which will be 5.4 times the economic benefit of traditional electrolysis of water for hydrogen production.

该研究为低成本制氢耦合生物质的高效高附加值电催化转化提供了一个新颖而富有前景的研究方向，这对推动质子交换膜电解水制氢技术和高附加值生物质催化转化的发展具有重要理论和实际意义。

论文信息

Efficient Conversion of Biomass to Formic Acid Coupled with Low Energy Consumption Hydrogen Production from Water Electrolysis

Dr. Wensi Tang, Dr. Lunan Zhang, Dr. Tianyu Qiu, Prof. Huaqiao Tan, Prof. Yonghui Wang, Dr. Wei Liu, Prof. Yangguang Li

文章的第一作者是东北师范大学的博士研究生唐文思和张路南。

Angewandte Chemie International Edition

DOI: 10.1002/anie.202305843