High-entropy alloys (HEAs) are near-equimolar alloys comprising five or more elements. In recent years, catalysis using HEAs has attracted considerable attention across various fields. Herein, we demonstrate the facile synthesis of nanoporous ultra-high-entropy alloys (np-UHEAs) with hierarchical porosity via dealloying. These np-UHEAs contain up to 14 elements, namely, Al, Ag, Au, Co, Cu, Fe, Ir, Mo, Ni, Pd, Pt, Rh, Ru, and Ti. Furthermore, they exhibit high catalytic activities and electrochemical stabilities in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in acidic media, superior to that of commercial Pt/graphene and IrO₂ catalysts. Our results offer valuable insights for the selection of elements as catalysts for various applications.

The global environment has been variously compromised leading to problems such as global warming and radioactive contamination. In this feature article, we will focus especially on materials for environmental remediation based on the concept of materials nanoarchitectonics. The topics are classified into three categories: removal and degradation of toxic substances including waste due to fossil fuel usage and organic pollutants (continuously arising problems), current emerging topics concerning oil spills and nuclear waste (current urgent problems), and advanced methods based on supramolecular chemistry and nanotechnology (including breakthroughs for future development).

A copper-and-zinc (Cu–Zn) alloy material was synthesized using a vacuum sealing method, in which evaporated zinc was reacted with copper film or nanoparticles to form a homogeneous Cu–Zn alloy. This alloy was evaluated as an electrocatalyst and/or cocatalyst for photocatalysis to selectively reduce carbon dioxide to formic acid. Based on the optimised alloy composition, the Cu₅Zn₈ catalyst exhibited efficient electrochemical CO₂ reduction. Furthermore, we constructed a photoelectrochemical (PEC) three-electrode system, in which the Cu₅Zn₈ film functioned as the cathode for CO₂ reduction in the dark and strontium titanate (SrTiO₃) served as the photoanode for water oxidation. The PEC system also selectively reduced CO₂ to formic acid with a faradaic efficiency of 79.11% under UV-light and the absence of an applied bias potential. SrTiO₃ particles decorated with nanoparticles of the Cu–Zn alloy also photocatalytically reduced CO₂ to formic acid under UV-light. Isotope trace analysis demonstrated that water served as the electron donor to produce oxygen and organic molecules under UV light, similar to photosynthesis in plants. The Cu–Zn alloy material developed in the present study is composed of ubiquitous and safe materials, and can catalyse CO₂ conversion by means of various kinds of renewable energies.