Study on bubble dynamic characteristics and mass transfer mechanism in photoelectrochemical water splitting for hydrogen production

doi:10.11949/0438-1157.20240348

Abstract

Abstract:

The long-term continuous growth of bubbles on the surface of the photoelectrode is an important factor affecting the efficiency of photoelectrochemical water splitting for hydrogen production. The effects of laser power and pressure in the cell on the evolution characteristics of bubbles and the mass transfer process at the gas-liquid interface were systematically studied by a multi-parameter simultaneous in-situ measurement and analysis method of photochemistry and bubble dynamics. The results demonstrate that bubbles under different laser powers and pressures follow similar growth rules before detachment. The gas mass yield reaches an extreme value at 80 kPa, indicating that appropriately lowering the pressure is beneficial to gas production. In addition, as the pressure decreases, the bubble detachment diameter increases and period shortens. By comparing force balance models considering different Marangoni forces, it is found that the force balance model considering both concentration Marangoni force and thermal Marangoni force has a prediction error of less than 5% for bubble detachment diameter and the concentration Marangoni force is the main factor affecting bubble detachment diameter under different pressures. Through solving the mass transfer coefficients, it can be found that the gas-liquid mass transfer is dominated by single-phase free microconvection under different pressure conditions in low photocurrent densities, but the effect of bubble-induced microconvection induced by expansion of gas-liquid interface on mass transfer is enhanced with the increase of photocurrent density.

Key words: photoelectrochemical water splitting, bubble, hydrogen production, pressure, mass transfer

摘要：

光电极表面长时间连续生长的气泡是影响光电分解水制氢效率的重要因素。利用光电化学与气泡动力学多参数同步原位测量分析方法，系统研究了激光功率和电解池内压力对气泡动力学特性和气液界面传质过程的影响。结果表明，不同激光功率和压力下的气泡在脱离之前遵循相似的生长规律。气体质量产率在80 kPa取得极值，表明适当降低压力有利于气体的产生。此外，随着压力降低气泡脱离直径增大，周期缩短。对比考虑不同Marangoni力的力平衡模型，发现同时考虑浓度Marangoni力和热Marangoni力的力平衡模型对气泡脱离直径的预测误差小于5%，浓度Marangoni力是不同压力下影响气泡脱离直径的主要因素。通过求解传质系数，发现在低光电流密度内，不同压力条件下气液传质以单相自然微对流为主，但随着光电流密度的增大，气液界面扩张引起的气泡诱导微对流传质作用增强。

关键词: 光电化学分解水, 气泡, 制氢, 压力, 传质

CLC Number:

O 643.3

Xinyi LUO, Qiang XU, Yonglu SHE, Tengfei NIE, Liejin GUO. Study on bubble dynamic characteristics and mass transfer mechanism in photoelectrochemical water splitting for hydrogen production[J]. CIESC Journal, 2024, 75(9): 3083-3093.

罗欣怡, 徐强, 佘永璐, 聂腾飞, 郭烈锦. 光电分解水制氢气泡动力学特性及其传质机理研究[J]. 化工学报, 2024, 75(9): 3083-3093.

Figures/Tables 12

Fig.1 Experimental platform for bubble dynamics and photoelectrochemical synchronous in-situ test in photoelectrochemical water splitting for hydrogen production

Table 1 Parameter settings for single bubble dynamics experiment

实验参数	数值
室温T/K	293.15
大气压p₀/kPa	97
实验系统压力p/kPa	60~97
电解液表面张力γ/(N·m^-1)	0.072
电解液密度ρ_L/(kg·m^-3)	1.0664×10³
电解液运动黏度ν_L/(m²·s^-1)	10^-6
激光光斑半径r_laser/nm	500
激光功率W/mW	8~12
外加偏压U（vs饱和Ag/AgCl）/V	0.2
电化学工作站采样频率f/s^-1	10³
高速摄像机拍摄帧率v/(帧·s^-1)	10³
高速摄像机分辨率	512×512
显微镜放大倍率	12.5

Fig.2 Curves of photocurrent under different laser powers and pressures

Fig.3 Correlation between photocurrent and bubble evolution on photoelectrode surface (W=12 mW and p=80 kPa)

Fig.4 Normalized bubble diameters at different laser powers and pressures

Fig.5 Changes of bubble detachment diameter and period with pressure

Fig.6 Variation of dynamic contact angle with time under different laser powers and pressures

Fig.7 Curves of variation of gas production rate with pressure

Fig.8 Forces on a single bubble in PEC water splitting reaction

Fig.9 Comparison of the actual measured bubble detachment diameters with the predicted values of force balance models

Fig.10 Transient behaviors of mass transfer coefficients under different laser powers and pressures

Fig.11 Variation of Average mass transfer coefficients with photocurrent density

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