Polymer electrolyte membrane water electrolyzers (PEMWEs) are considered as the most suitable generators for the green hydrogen production on a large scale. The porous transport layer (PTL) in the anode, which most commonly consists of titanium (Ti), is a crucial component to reduce contact resistance and to ensure effective mass transport from or to the catalyst layer. A large variety of PTLs which are commercially available such as Ti mesh, Ti felt and sintered Ti powder, etc., have been widely studied and developed to facilitate the PEMWE applications. However, the formation of TiO_x on PTL, which often occurs under the conditions of the electrocatalytic oxygen evolution reaction (OER), leads to serious performance degradation of PEMWE. Surface modifications of Ti-based PTLs by precious metals (e.g. Au, Pt, Ir) are thus critical to avoid the oxidization of Ti material. Especially for the large-scale applications, there is clearly a need to establish a trade-off between the electrolysis performance and the use of precious metals.

Herein, we present a systematic study of PTL surface modification for effective and robust OER in a PEMWE. A magnetron sputtering method is developed to deposit a thin film of Pt (or Ir) on a Ti felt. Benefiting from the highly precise control of our developed magnetron sputtering method, the loading of noble metal with unform distribution is decreased to 0.04 mg cm^-2. For comparation, a commercial Pt-coated PTL via a traditional electrochemical deposition is studied, and the Pt loading is near 0.1 mg cm^-2. Our results indicate that compared with the commercial PTL and the identical loading Ir-coated PTL, the home-made Pt-modified Ti felt exhibits the highest electrical conductivity (0.261 mΩ cm), and the cell voltage decreases to 1.78V at 2 A cm⁻² and 80°C when using Nafion^® 115 membrane. Moreover, based on a 200-h accelerated stability test, no degradation is observed from the cell with sputtering-Pt Ti felt, demonstrating its outstanding stability. Obviously, the cell performance is comparable to the best performance reported in literature. The SEM observations revealed that the dense and uniform structure of sputtering Pt which can minimize the Pt dissolution. The AC impedance measurements further indicate that the water, gaseous oxygen and electron transport can be improved significantly during electrolysis. Future work will be conducted to establish the effective synergetic mechanism between the Pt-coated layer of PTL and the catalyst layer, and to find the design strategies for the high-performance, low-cost, and long-term stable PTLs.