Design Of Metallic Glass Catalysts For Hydrogen Evolution Reaction

Hydrogen is a clean energy carrier that could replace fossil fuels and support future rapid development,but its sustainable production remains a significant challenge.Water electrolysis,a promising hydrogen production pathway,refers to the electrochemical process under a sufficient cell voltage where hydrogen evolution reaction(HER)takes place at the cathode and oxygen evolution reaction at the anode.Highly performing HER catalysts are required to accelerate the reaction with minimum energy input.The best HER catalysts are based on scarce and expensive Pt,making the development of low-cost yet highly efficient catalysts an important target.Although many Earth-abundant catalysts that display outstanding apparent activity have emerged over the past decades,the development of new HER catalysts with the guidance of novel design strategies never ceases.Metallic glasses(MGs),or amorphous alloys,are novel metastable materials that uniquely combine metal characteristics with a disordered atomic structure and therefore exhibit a wealth of exotic properties.In particular,due to a high density and diversity of low-coordination surface atomic sites,widely tunable compositions,and a homogeneous structure,they have received extensive attention as both real and model catalysts since 1980s,and recent years have also witnessed the rise in using MGs as HER catalysts.However,their HER catalytic performance is still rather limited even with extravagantly high precious metal loadings.More importantly,there is a lack of catalyst design strategies for MGs.This dissertation aims to address the above issues by proposing novel design strategies for MG HER catalysts,which mainly involves alloying and nanostructuring.The first part introduces the design strategy for a MG thin film catalyst that is intrinsically active for HER in acidic media.Although this strategy exploits the use of Ir for the improvement of intrinsic activity,the Ir loading is lowered to only 8.14?g cm^–2 by reducing the film thickness on a Si substrate to 15 nm with a low-Ir content Ir Ni Ta MG.The Ir Ni Ta/Si electrode drives the current density of 10 m A cm^–2 under an overpotential of 99 m V,has a small Tafel slope of 35 m V dec^–1,and displays catalytic stability superior to similar Ir/Si and Pt/Si electrodes.Its atomically flat surface also benefits the estimation of turnover frequency which quantifies intrinsic activity.It has been revealed through comparison that the Ir Ni Ta MG film is among the most intrinsically active HER catalysts,outperforming all reported MGs,representative Mo S₂-based catalysts,phosphides,and some other precious-metal-containing catalysts.Such outstanding performance is attributed to the novel alloy system and amorphous structure.The second part demonstrates the design strategy for MG ribbon catalysts that are highly active and stable for HER in alkaline media.This strategy combines Pt microalloying and surface dealloying with hydrofluoric acid(HF)treatment to fabricate Ni-based MG catalysts with nanoporous surface structures.The as-obtained nanoporous Ni Zr(Pt)MG ribbon shows an activity that is more than 17000 times that of the untreated Ni Zr MG ribbon in terms of the current density achieved at an overpotential of 50 m V.It can drive the current density of 10 m A cm^–2 under an overpotential of 32 m V and has a Tafel slope of 50.7 m V dec^–1.Another highly active catalyst is nanoporous Ni Zr(Mo Pt)MG ribbon,which has an overpotential of 44 m V but a smaller Tafel slope of 41.6 m V dec^–1.Only Pt microalloying or surface dealloying cannot achieve such a huge improvement in activity.The nanoporous MG ribbons also show remarkable stability for HER and are mechanically flexible for use as self-supported electrodes.