基于水电解制氢的梯度多孔传输层中气液流动可视化实验研究

doi:10.11949/0438-1157.20231165

摘要/Abstract

摘要：

在电解水制氢的过程中，多孔电极内的孔隙会发生气泡阻塞现象，这会妨碍气体扩散以及电解液在多孔电极内的流动，从而导致电极传质电阻的增加，进而影响电解水制氢的速率和能耗。采用3D金属打印技术制备了LSL-PTL、MMM-PTL和SLS-PTL三种规则的镍铁合金电极扩散层，进行了可视化的水电解实验，定量地记录了不同电流密度下梯度多孔传输层中气液两相流动的变化，包括气泡形态、孔隙含气率和气泡脱离速率等参数，研究扩散层梯度对气液传质过程的影响，并分析了不同电极梯度结构对电解过程中阻抗和过电位的影响。实验结果显示，与SLS-PTL和MMM-PTL相比，LSL-PTL的梯度结构从催化层即逐渐增大孔隙尺寸，始终保持较低的容积含气率，可以加速气泡在扩散层中的迁移，使气液交换更加频繁，有效减小气液传质阻力，并获得更低的传质阻抗和电解过电位，三种梯度电极在相同电流密度下的电解电势关系为 $E L S L < E M M M < E S L S$ 。因此，在水电解中采用LSL-PTL梯度的扩散层可以提高制氢效率，减少能耗损失。这项研究为水电解制氢中气液传质过程的主动控制和电解池多孔传输层的结构设计提供了直观依据，对电解水制氢技术的进一步发展具有积极推动作用。

关键词: 水电解, 多孔传输层, 梯度结构, 制氢, 气液两相流

Abstract:

During the process of electrolyzing water to produce hydrogen, the pores in the porous electrode will be blocked by bubbles, which will hinder gas diffusion and the flow of electrolyte in the porous electrode, resulting in an increase in the mass transfer resistance of the electrode. This in turn affects the rate and energy consumption of hydrogen production through electrolysis of water. Three regular shaped diffusion layers of nickel-iron alloy electrodes, LSL-PTL, MMM-PTL and SLS-PTL, were fabricated by 3D metal printing and visualized for water electrolysis experiments. In the experiments, the changes of gas-liquid two-phase flow in the gradient porous transport layer at different current densities were quantitatively recorded, including parameters such as bubble morphology, pore gas content and bubble detachment rate. The effects of the gradient of the diffusion layer on the gas-liquid mass transfer process were investigated, and the effects of different electrode gradient structures on the impedance and overpotential during electrolysis were analyzed. The experimental results show that compared with the two gradient structures of SLS-PTL and MMM-PTL, the gradient structure of LSL-PTL, i.e., gradually increasing the pore size from the catalytic layer, always maintains a lower volumetric gas content. It can accelerate the migration of gas bubbles in the diffusion layer, make the gas-liquid exchange more frequent, and effectively reduce the gas-liquid mass transfer resistance. Moreover, a lower mass transfer impedance and electrolytic overpotential can be obtained by using the diffusion layer with this gradient, and the relationship of electrolytic potentials of the three gradient electrodes at the same current density is $E L S L < E M M M < E S L S$ . Therefore, a diffusion layer with LSL-PTL gradient in water electrolysis can improve the hydrogen production efficiency and reduce the energy loss. This study provides an intuitive basis for the active control of the gas-liquid mass transfer process in water electrolysis for hydrogen production and the structural design of the porous transport layer in the electrolytic cell, which will have a positive impact on the further development of electrolytic water hydrogen production technology.

Key words: water electrolysis, porous transport layer, gradient structure, hydrogen production, gas-liquid flow

中图分类号:

TQ 116.21

刘志鹏, 赵长颖, 吴睿, 张智昊. 基于水电解制氢的梯度多孔传输层中气液流动可视化实验研究[J]. 化工学报, 2024, 75(2): 520-530.

Zhipeng LIU, Changying ZHAO, Rui WU, Zhihao ZHANG. Experimental study of gas-liquid flow visualization in gradient porous transport layers based on hydrogen production by water electrolysis[J]. CIESC Journal, 2024, 75(2): 520-530.

图/表 14

图1 AEMWE电极结构及电解原理

Fig.1 Structure of AEMWE electrodes

图2 三种梯度多孔传输层中的层结构

Fig.2 Porous transport layer structure with three gradients

表1 三种不同梯度的多孔传输层详细参数

Table 1 Detailed parameters of three different gradients of the PTL

孔隙边长依次为0.8、1.0和1.2 mm

每层孔隙的深度均为1.8 mm

扩散层孔隙度25.67%

MMM-PTL

扩散层孔隙尺寸从催化层向外各处均匀一致

孔隙边长1.01 mm

孔隙深度5.4 mm

扩散层孔隙度25.67%

SLS-PTL

扩散层孔隙尺寸从催化层界面向外递减

孔的边长依次为1.2、1.0和0.8 mm

每层孔隙的深度均为1.8 mm

扩散层孔隙度25.67%

图3 实验台

Fig.3 AEMWE experimental setup

图4 0.1 A/cm2电流密度下催化层与扩散层界面处气泡生成与脱离

Fig.4 Bubble generation and detachment at the interface of catalytic and diffusion layers at 0.1 A/cm2 current density

图5 LSL-PTL、MMM-PTL、SLS-PTL在0.1 A/cm2的电流下HER产生的气泡在多孔传输层中的形态（白色虚线为扩散层中不同梯度孔隙分界）

Fig.5 Morphology of bubbles generated by HER in the porous transport layer at a current of 0.1 A/cm2 for LSL-PTL, MMM-PTL, and SLS-PTL (the white dashed line represents the boundary between pores with different gradients in the diffusion layer)

图6 0.1 A/cm2电流密度下LSL-PTL扩散层内气泡形态和位置随时间变化(a)及气泡脱离直径分布情况(b)

Fig.6 (a) Sets of photographs demonstrating the typical bubble removal processes releasing from LSL-PTL at 0.1 A/cm2 current density; (b) Distribution of the diameters of hydrogen bubbles that detached from LSL-PTL at 0.1 A/cm2 current density

图7 0.1 A/cm2电流密度下MMM-PTL扩散层内气泡形态和位置随时间变化(a)及气泡脱离直径分布情况(b)

Fig.7 (a) Sets of photographs demonstrating the typical bubble removal processes releasing from MMM-PTL at 0.1 A/cm2 current density; (b) Distribution of the diameters of hydrogen bubbles that detached from MMM -PTL at 0.1 A/cm2 current density

图8 0.1 A/cm2电流密度下SLS-PTL扩散层内气泡形态和位置随时间变化(a)及气泡脱离直径分布情况(b)

Fig.8 (a) Sets of photographs demonstrating the typical bubble removal processes releasing from SLS-PTL at 0.1 A/cm2 current density; (b） Distribution of the diameters of hydrogen bubbles that detached from SLS-PTL at 0.1 A/cm2 current density

图9 扩散层中一个脱离周期内的气泡演化过程和容积含气率变化

Fig.9 Volumetric gas content in the diffusion layer during one detachment cycle versus time at different current densities

图10 扩散层中气泡释放周期随电流密度的变化

Fig.10 Variation of bubble release period with current density in the diffusion layer

图11 不同电流密度条件下气泡脱离时刻的临界β0及气泡脱离时刻的最大容积含气率β

Fig.11 Maximum β0 at the moment of bubble detachment and maximum volumetric gas content β at the moment of bubble detachment for different current density conditions

图12 LSL-PTL、MMM-PTL、SLS-PTL内的气泡受力情况

Fig.12 The bubble forces in LSL-PTL, MMM-PTL, SLS-PTL

图13 LSL-PTL、MMM-PTL和SLS-PTL电极的极化曲线(a)、Tafel斜率图(b)、EIS测试Nyquist图(c)

Fig.13 (a) Polarization curve of LSL-PTL, MMM-PTL and SLS-PTL electrodes; (b) Tafel plots for LSL-PTL, MMM-PTL and SLS-PTL electrodes; (c) EIS Nyquist plots of LSL-PTL, MMM-PTL and SLS-PTL electrodes

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