Hydride metallenes show great potential for hydrogen-related catalytic applications due to favorable electronic structures modulated by interstitial hydrogen atoms and large active surface areas of metallenes. Metallene nanostructures generally have compressive strain relative to bulk, which can affect both the stability and the catalytic behavior of hydride metallenes but in general cannot be controlled. Here, we demonstrate highly stable PdH x metallenes with a tensile strained Ru surface layer and reveal the spatial confinement effect of the Ru skin by multiple spectroscopic characterizations and molecular dynamics simulations. These PdH x @Ru metallenes with a 4.5% expanded Ru outer layer exhibit outstanding alkaline hydrogen evolution reaction activity with a low overpotential of 30 mV at 10 mA cm–2 and robust stability with negligible activity decay after 10,000 cycles, which are superior to commercial Pt/C and most reported Ru-based electrocatalysts. Control experiments and first-principles calculations reveal that the tensile strained Ru outer layer lowers the energy barrier of H2O dissociation and provides a moderate hydrogen adsorption energy.

Acidic oxygen evolution reaction (OER) catalysts face the fundamental challenge of the trade-off between activity and durability that has not yet been well addressed. Herein, we integrate high activity of nanoparticles and good stability of bulk materials into a "macro-nano" catalyst through twodimensional self-assembling of unconventional fcc phase Ru 3 Ir nanocrystals. Such catalysts deliver a low overpotential of 190 mV at 10 mA cm −2 and stably maintain this over 400 h or 10,000 potential cycles for acidic OER, surpassing previously reported metallic-based catalysts. Operando X-ray absorption spectroscopy and DFT calculations reveal that the high activity is derived from self-reconstructed surface Ru 3 IrO x species during OER, which are electronically modulated by the fcc-Ru 3 Ir substrate and lower the energy barrier of the potential-determining O* → OOH* step. Control experiments reveal that two-dimensional self-assembled structures significantly enhance the corrosion resistance ability of 2D fcc-Ru 3 Ir by inhibiting the excessive dissolution of surface Ru 3 IrO x species during the OER process. This nano-to-macro strategy may provide a guideline for designing efficient and robust catalysts for acidic OER and beyond.

Au/Pd heterojunction@mesoporous SiO2 yolk–shell NPs exhibit extremely high stability for the plasmon-enhanced catalytic reduction of p-nitrophenol under visible light irradiation.