The sluggish kinetics of oxygen evolution reaction (OER) and high iridium loading in catalyst coated membrane (CCM) are the key challenges for practical proton exchange membrane water electrolyzer (PEMWE). Herein, we demonstrate high-surface-area nano-metal diborides as promising supports of iridium-based OER nanocatalysts for realizing efficient, low-iridium-loading PEMWE. Nano-metal diborides are prepared by a novel disulphide-to-diboride transition route, in which the entropy contribution to the Gibbs free energy by generation of gaseous sulfur-containing products plays a crucial role. The nano-metal diborides, TaB₂ in particular, are investigated as the support of IrO₂ nanocatalysts, which finally forms a TaO_x/IrO₂ heterojunction catalytic layer on TaB₂ surface. Multiple advantageous properties are achieved simultaneously by the resulting composite material (denoted as IrO₂@TaB₂), including high electrical conductivity, improved iridium mass activity and enhanced corrosion resistance. As a consequence, the IrO₂@TaB₂ can be used to fabricate the membrane electrode with a low iridium loading of 0.15 mg cm⁻², and to give an excellent catalytic performance (3.06 A cm⁻²@2.0 V@80 ^oC) in PEMWE―the one that is usually inaccessible by unsupported Ir-based nanocatalysts and the vast majority of existing supported Ir-based catalysts at such a low iridium loading.

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

Liquid/gas diffusion layers (LGDLs), which are located between the catalyst layer (CL) and bipolar plate (BP), play an important role in enhancing the performance of water splitting in proton exchange membrane electrolyzer cells (PEMECs). They are expected to transport electrons, heat, and reactants/products simultaneously with minimum voltage, current, thermal, interfacial, and fluidic losses. In this study, the thin titanium-based LGDLs with straight-through pores and well-defined pore morphologies are comprehensively investigated for the first time. The novel LGDL with a 400 μm pore size and 0.7 porosity achieved a best-ever performance of 1.66 V at 2 A cm⁻² and 80 °C, as compared to the published literature. The thin/well-tunable titanium based LGDLs remarkably reduce ohmic and activation losses, and it was found that porosity has a more significant impact on performance than pore size. In addition, an appropriate equivalent electrical circuit model has been established to quantify the effects of pore morphologies. The rapid electrochemical reaction phenomena at the center of the PEMEC are observed by coupling with high-speed and micro-scale visualization systems. The observed reactions contribute reasonable and pioneering data that elucidate the effects of porosity and pore size on the PEMEC performance. This study can be a new guide for future research and development towards high-efficiency and low-cost hydrogen energy.

The properties of porous transport layers (PTL) in electrolysis devices and their effects on cell performance have been studied extensively in recent literature. This paper provides a detailed analysis with regards to the transport in the catalyst layer (CL). The work demonstrated that the catalyst loading affects the sensitivity of electrolysis performance to PTL properties, particularly those of the PTL surface in contact with the CL. It was demonstrated that upon reducing catalyst loading, PTL properties had an increased effect on the performance of PEMWE cells. While we observed mild performance variations among PTLs when using a high anode catalyst loading, strong correlations between PTL surface properties and cell performance existed at a low catalyst loading. PTL properties affected performance by influencing the in-plane conductivity and permeability of the CL. The variation of apparent exchange current density and apparent CL bubble coverage with the stoichiometric flow rate was studied at low anode feed rates. This led to the emergence of a PTL grain size effect on apparent bubble coverage at high catalyst loading. We provide a descriptive analysis of the phenomena causing voltage losses in PEMWE devices. These findings are important for electrochemical modeling and designing the PTL/CL interface.