As opposed to the common monotonic relaxation process of glasses, the Kovacs memory effect describes an isothermal annealing experiment, in which the enthalpy and volume of a preannealed glass first increases before finally decreasing toward equilibrium. This interesting behavior has been observed for many materials and is generally explained in terms of heterogeneous dynamics. In this Letter, the memory effect in a model Au-based metallic glass is studied using a high-precision high-rate calorimeter. The activation entropy ($S^{*}$) during isothermal annealing is determined according to the absolute reaction rate theory. We observe that the memory effect appears only when the second-annealing process has a large $S^{*}$. These results indicate that a large value of $S^{*}$ is a key requirement for observation of the memory effect and this may provide a useful perspective for understanding the memory effect in both thermal and athermal systems.

A core–shell-structured bimetallic nanoporous PtCu catalyst with a high non-noble metal content (Cu: ∼55 at%) and uniformly distributed ultrafine ligaments (∼3 nm) is fabricated by one-step dealloying a well-designed Pt₄Cu₂₁Mn₇₅ single-phase ternary precursor in 1 M (NH₄)₂SO₄ aqueous solution. The one-step dealloying involves a two-step corrosion process: one is fast dealloying the most active Mn from the ternary alloy to form nanoporous PtCu and the next step is a slow dealloying process which would slowly dissolve Cu from the PtCu alloy ligament surface forming a core–shell-structured nanoporous PtCu alloy with a Pt shell and a PtCu alloy core. Electrochemical measurements manifest that the core–shell-structured nanoporous PtCu exhibits greatly enhanced catalytic activity towards the electro-oxidation of methanol and formic acid compared with both nanoporous Pt and the state-of-the-art Pt/C catalyst. With evident advantages of facile preparation and enhanced catalytic performance, the nanoporous core–shell-structured PtCu catalyst is very promising as an anode catalyst in fuel cells. Moreover, this strategy (i.e., dealloying well-designed Mn-based ternary alloys) can also be used to fabricate other uniform nanoporous core–shell-structured alloys such as the nanoporous NiCu alloy.

An electrode with low performance or limited endurance for water splitting hydrogen generation has been the key limitation for application of hydrogen in contemporary clean-energy technologies. In this paper, an Al₈₀Ni₆Co₃Mn₃Y₅Au₃ metallic glass ribbon with outstanding catalytic activity in the hydrogen evolution reaction (HER) in acidic solutions is fabricated for the first time. Its overpotential is about 70 mV @ 10 mA cm⁻² and Tafel slope is about 39 mV dec⁻¹, which are comparable to those of commercial noble Pt/C electrodes (33 mV @ 10 mA cm⁻² and 38 mV dec⁻¹). Such a high catalytic reactivity is attributed to the synergic effect of multiple elements that disperse atomically homogeneously on the nanoporous surface. The outstanding catalytic activity persists and even becomes much better over a long-time reaction, which is attributed to the formation of a protective Au-rich layer in the interface. The Al-based metallic glass ribbon is flexible with high yield strength, large elasticity and good electrical conductivity, which are desirable and promising characteristics for a free-standing catalytic electrode in the HER.