Increase 50-time catalyst mass activity from revealing true reactions in proton exchange membrane electrolysis.

Novel LGDLs remarkably reduce losses and reveals unprecedented rapid electrochemical reactions.

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In this study, a novel titanium thin LGDL with well-tunable pore morphologies was developed by employing nano-manufacturing and was applied in a standard PEMEC. The LGDL tests show significant performance improvements. The operating voltages required at a current density of 2.0 A/cm 2 were as low as 1.69 V, and its efficiency reached a report high of up to 88%. The new thin and flat LGDL with well-tunable straight pores has been demonstrated to remarkably reduce the ohmic, interfacial and transport losses. In addition, well-tunable features, including pore size, pore shape, pore distribution, and thus porosity and permeability, will be very valuable for developing PEMEC models and for validation of its simulations with optimal and repeatable performance. The LGDL thickness reduction from greater than 350 µm of conventional LGDLs to 25 µm will greatly decrease the weight and volume of PEMEC stacks, and represents a new direction for future developments of low-cost PEMECs with high performance.

a b s t r a c tThis paper presents a comprehensive computational model for the proton exchange membrane (PEM) electrolyzer cells, which have attracted more attention for renewable energy storage and hydrogen production. A new ohmic loss model of a PEM electrolyzer cell has been developed and the influence of different operating conditions and physical design parameters on its performance has been investigated, including operating temperature, pressure, exchange current density, electrode thickness, membrane thickness and interfacial resistance. The interfacial resistance between the membrane and electrode has been found to play an important part for electrolyzer performance and an overpotential is increased significantly with the interfacial resistance. At a current density of 1.5 A/cm 2 , the performance loss due to the interfacial resistance between the membrane and electrode comprises 31.8% of the total ohmic loss. Thickness changes in either electrode or membrane also have significant impacts on the electrolyzer performance mainly due to their contributions to the diffusion overpotential and ohmic loss. Increasing the operating temperature will result in lower electrolyzer overpotential, while increasing the operating pressure will lead to higher electrolyzer overpotential, which is mainly controlled by the open circuit voltage. Results obtained from the present model will provide a comprehensive understanding of design parameter effects and consequently improve the design/performance in a PEM electrolyzer cell.

Visualization investigation the oxygen bubble evolution and dynamics reveals the real phenomena inside an operating proton exchange membrane electrolyzer cell.

A low-cost additive manufacturing technology, electron beam melting (EBM), is employed for the first time to fabricate titanium liquid/gas diffusion media with high-corrosion resistances and well-controlled multifunctional parameters, including two-phase transport and high electric/thermal conductivities. Its application in proton exchange membrane electrolyzer cells (PEMECs) has been investigated in-situ with modular galvano (MG) and galvano electrochemical impedance spectroscopy (GEIS) and characterized ex-situ with SEM and XRD. Compared with conventional woven and sintered liquid/gas diffusion layers (LGDLs), much better performance is obtained with EBM-fabricated LGDLs due to a significant reduction of ohmic losses. The EBM technology components exhibited several distinct advantages in fabricating LGDLs: well-controllable pore morphology and structure, rapid prototyping, fast manufacturing, highly customizable design, and economic. In addition, by taking advantage of additive manufacturing, it is possible to fabricate complicated three-dimensional designs of virtually any shape from a digital model into one single solid object faster, cheaper, and easier, especially for titanium components. More importantly, this development will provide LGDLs with well-controllable pore morphologies, which will be valuable to develop sophisticated models of PEMECs with optimal and repeatable performance. Furthermore, it could lead to a manufacturing solution that greatly simplifies the PEMEC/fuel cell components.

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