This paper introduces the formation mechanism of the hydrogen-in-oxygen issue in alkaline electrolyzers.It provides a detailed analysis of the key factors driving the increase in hydrogen content within the oxygen stream,with a focused discussion on the sensitivity of hydrogen levels to these variables.Corresponding control methods for mitigating this issue are presented based on the analysis.Furthermore,future research directions for addressing the hydrogen-in-oxygen problem are outlined.
GötzM, LefebvreJ, MörsF, et al. Renewable Power-to-Gas:A technological and economic review[J]. Renewable Energy, 2016, 85:1371-1390.
[3]
SchröderV, EmontsB, JanßenH, et al. Explosion limits of hydrogen/oxygen mixtures at initial pressures up to 200 bar[J]. Chemical Engineering & Technology:Industrial Chemistry-Plant Equipment-Process Engineering-Biotechnology, 2004, 27(8):847-851.
[4]
WiedenmannD, KellerL, HolzerL, et al. Three-dimensional pore structure and ion conductivity of porous ceramic diaphragms[J]. AIChE Journal, 2013, 59(5):1446-1457.
[5]
KraglundM R, AiliD, JankovaK, et al. Zero-gap alkaline water electrolysis using ion-solvating polymer electrolyte membranes at reduced KOH concentrations[J]. Journal of the Electrochemical Society, 2016, 163(11):F3125-F3131.
[6]
HaugP. Experimental and theoretical investigation of gas purity in alkaline water electrolysis[M]. Munich: Verlag Dr Hut, 2019.
[7]
HysaG, AnttilainenT, RuuskanenV, et al. Modelling and study of shunt currents in an industrial alkaline water electrolyser with various number of cells in series[J]. IET Renewable Power Generation, 2025, 19(1):e70112.
[8]
WuR, HuZ, ZhangH, et al. Bubbles in porous electrodes for alkaline water electrolysis[J]. Langmuir, 2023, 40(1):721-733.
[9]
LiW, SunZ, YeX, et al. Ultra-thin PPS mesh-based PSF-ZrO2 composite diaphragm for efficient electrolysis of water for hydrogen production[J]. International Journal of Hydrogen Energy, 2024, 81:918-926.
[10]
TrinkeP, HaugP, BraunsJ, et al. Hydrogen crossover in PEM and alkaline water electrolysis:Mechanisms,direct comparison and mitigation strategies[J]. Journal of the Electrochemical Society, 2018, 165(7):F502-F513.
[11]
BarrosR L G, KraakmanJ T, SebregtsC, et al. Impact of an electrode-diaphragm gap on diffusive hydrogen crossover in alkaline water electrolysis[J]. International Journal of Hydrogen Energy, 2024, 49:886-896.
OikonomidisS, RamdinM, MoultosO A, et al. Transient modelling of a multi-cell alkaline electrolyzer for gas crossover and safe system operation[J]. International Journal of Hydrogen Energy, 2023, 48(88):34210-34228.
[14]
ChatenetM, PolletB G, DekelD R, et al. Water electrolysis:From textbook knowledge to the latest scientific strategies and industrial developments[J]. Chemical Society Reviews, 2022, 51(11):4583-4762.
[15]
DemnitzM, van der SchaafJ, de GrootM T. Alkaline water electrolysis beyond 3 A/cm2 using catalyst coated diaphragms[J]. Journal of the Electrochemical Society, 2025, 172(1):014504.
[16]
SerhiichukD. Toward new polymer electrolyte membranes for advanced alkaline water electrolysis[D]. Kgs Lyngby: Technical University of Denmark, 2023.
[17]
LeeH I, ChoH S, KimM, et al. The structural effect of electrode mesh on hydrogen evolution reaction performance for alkaline water electrolysis[J]. Frontiers in Chemistry, 2021, 9:787787.
EhlersJ C, Feidenhans’lA A, TherkildsenK T, et al. Affordable green hydrogen from alkaline water electrolysis:Key research needs from an industrial perspective[J]. ACS Energy Letters, 2023, 8(3):1502-1509.
BraunsJ, TurekT. Model-based analysis and optimization of pressurized alkaline water electrolysis powered by renewable energy[J]. Journal of the Electrochemical Society, 2023, 170(6):064510.
BraunsJ, TurekT. Experimental evaluation of dynamic operating concepts for alkaline water electrolyzers powered by renewable energy[J]. Electrochimica Acta, 2022, 404:139715.
[25]
DavidM, BianchiF, Ocampo-MartinezC, et al. Model-based control design for H2 purity regulation in high-pressure alkaline electrolyzers[J]. Journal of the Franklin Institute, 2021, 358(8):4373-4392.
[26]
WangY, HuoX, PengM, et al. Superhydrophilic polyphenylene sulfide membrane with enhanced ion transfer for alkaline water electrolysis[J]. International Journal of Hydrogen Energy, 2024, 65:872-880.
[27]
SeetharamanS, RavichandranS, DavidsonD J, et al. Polyvinyl alcohol based membrane as separator for alkaline water electrolyzer[J]. Separation Science and Technology, 2011, 46(10):1563-1570.
[28]
SchneiderL P C, DhriouaM, UllmerD, et al. Advancements in hydrogen production using alkaline electrolysis systems:A short review on experimental and simulation studies[J]. Current Opinion in Electrochemistry, 2024, 47:101552.