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Water electrolyzers will ensure energy security and power grid stability in energy systems based on fluctuating renewable energy sources such as wind power and photovoltaics. In this article, the effects of volatile energy generation on the operating conditions within polymer electrolyte membrane water electrolyzers are investigated. Based on experiments on a 100 kW el test station, it is concluded that isothermal and isobaric operation is unattainable and temperature deviations between −7 K and 3 K from their setpoint are observed. Pressure control on the hydrogen side is more challenging than on the oxygen side. Temperature decreases due to non-ideal temperature control overall decrease the mean efficiency during dynamic operation as compared to steady-state, with wind power reaching 73.70 % LHV and solar power yielding 71.90 % LHV. Finally, adaptions of electrolyzer designs and operation strategies are discussed, that could reduce negative effects of system dynamics on process efficiency. • System analysis is performed to identify inherent bottlenecks to dynamic operation. • Experimental investigation of characteristic load profiles on 100 kW el electrolyzer. • Evaluation of operation profiles reveals PV to be more challenging than wind power. • Dynamic operation appears to lower the overall hydrogen production efficiency. • Potential strategies to mitigate negative effects of system dynamics are discussed. [ABSTRACT FROM AUTHOR]

Water electrolysis will be an essential element of the future energy system, with hydrogen serving as a climate-friendly energy storage medium. To make electrolyzers suitable for market penetration at scale, the cost of manufacturing megawatt electrolyzers must be minimized, with no detrimental effects to their performance and lifetime. Here we show a facile and cost-effective manufacturing method to produce one-piece Ti-based bipolar plates. Low-cost and commercially and readily available feedstock materials (blank sheets, expanded metals and nonwovens) are positively joined using an innovative welding process, diffusion bonding. This approach reduces the contact resistances that can occur with multi-part bipolar plates by around 75%, reducing the number of components and therefore significantly simplifying stack assembly. Ex-situ tests on the contact pressure distribution on the active cell surface reveal a homogeneous pattern with values of about 3.75 MPa (± 1.25 MPa). In a first proof-of-concept, a five-cell short stack with a 100 cm2 active cell area, average cell voltages of 1.71 V at 2 A cm−2 could be achieved using our new stack concept. • Detailed insight into the plate design, construction, production and verification. • Main feature of the novel bipolar plate is the one-piece-approach. • Development of a welding-based production process; elimination of contact resistances. • Approach increases the reliability and decreases the duration of the stack assembly. [ABSTRACT FROM AUTHOR]

This study outlines an approach to identifying the difficulties associated with the benchmarking of alkaline single cells under real electrolyzer conditions. A challenging task in the testing and comparison of different catalysts is obtaining reliable and meaningful benchmarks for these conditions. Negative effects on reproducibility were observed due to the reduction in conditioning time. On the anode side, a stable passivation layer of NiO can be formed by annealing of the Ni foams, which is even stable during long-term operation. Electrical contact resistance and impedance measurements showed that most of the contact resistance derived from the annealed Ni foam. Additionally, analysis of various overvoltages indicated that most of the total overvoltage comes from the anode and cathode activation overpotential. Different morphologies of the substrate material exhibited an influence on the performance of the alkaline single cell, based on an increase in the ohmic resistance. • Identifying difficulties associated with the benchmarking of alkaline single cells. • Negative effects on reproducibility observed due to reduction in conditioning time. • A stable passivation layer of NiO on anode during long-term operation. • Most overvoltage comes from the anode and cathode activation overpotential. • Morphologies of substrate material exhibited an key influence on the performance. [ABSTRACT FROM AUTHOR]