Electrocatalytic hydrogen evolution in alkaline and neutral media offers the possibility of adopting platinum‐free electrocatalysts for large‐scale electrochemical production of pure hydrogen fuel, but most state‐of‐the‐art electrocatalytic materials based on nonprecious transition metals operate at high overpotentials. Here, a monolithic nanoporous multielemental CuAlNiMoFe electrode with electroactive high‐entropy CuNiMoFe surface is reported to hold great promise as cost‐effective electrocatalyst for hydrogen evolution reaction (HER) in alkaline and neutral media. By virtue of a surface high‐entropy alloy composed of dissimilar Cu, Ni, Mo, and Fe metals offering bifunctional electrocatalytic sites with enhanced kinetics for water dissociation and adsorption/desorption of reactive hydrogen intermediates, and hierarchical nanoporous Cu scaffold facilitating electron transfer/mass transport, the nanoporous CuAlNiMoFe electrode exhibits superior nonacidic HER electrocatalysis. It only takes overpotentials as low as ≈240 and ≈183 mV to reach current densities of ≈1840 and ≈100 mA cm−2 in 1 m KOH and pH 7 buffer electrolytes, respectively; ≈46‐ and ≈14‐fold higher than those of ternary CuAlNi electrode with bimetallic Cu–Ni surface alloy. The outstanding electrocatalytic properties make nonprecious multielemental alloys attractive candidates as high‐performance nonacidic HER electrocatalytic electrodes in water electrolysis.

In reviewing the results reported for copper oxidation at intermediate temperatures from 573 to 1173 K, the oxidation mechanism at the lower part of this temperature range and the reason for the change in activation energy with decreasing the temperature remain unclear. To make it clear, copper oxidation is studied at 623-1073 K under 0.1 MPa O 2 using a commercial 99.9999% pure copper. The oxidation kinetics is essentially parabolic, and the activation energy decreases from 111 kJ/mol at 873-1073 K to 40 kJ/mol at 623-773 K.

To clarify the oxidation mechanism of Cu 2 O to CuO, Cu 2 O oxidation was studied at 600-1050 • C under 1 atm O 2 . The Cu 2 O specimens were prepared through completely oxidizing 99.99999 and 99.5% pure copper at 1000 • C in an Ar + 1% O 2 atmosphere. The oxidation kinetics of Cu 2 O specimens prepared from both purity levels followed the logarithmic law, not the parabolic law or the cubic law as reported in the literature. The activation energy for Cu 2 O oxidation is relatively high in the lower-temperature range, but becomes very small or even negative at higher temperatures. The logarithmic oxidation rate law can be explained by Davies et al.'s model related to grain-boundary diffusion in the oxide layers. The very small or negative activation energies in the higher-temperature range can be attributed to the very small thermodynamic driving force and the fast lateral growth of CuO grains related to a sintering effect. The influence of small amount of impurities is also discussed.

Alloying techniques show genuine potential to develop more effective catalysts than Pt for oxygen reduction reaction (ORR), which is the key challenge in many important electrochemical energy conversion and storage devices, such as fuel cells and metal‐air batteries. Tremendous efforts have been made to improve ORR activity by designing bimetallic nanocatalysts, which have been limited to only alloys of platinum and transition metals (TMs). The Pt‐TM alloys suffer from critical durability in acid‐media fuel cells. Here a new class of mesostructured Pt–Al catalysts is reported, consisting of atomic‐layer‐thick Pt skin and Pt3Al or Pt5Al intermetallic compound skeletons for the enhanced ORR performance. As a result of strong Pt–Al bonds that inhibit the evolution of Pt skin and produce ligand and compressive strain effects, the Pt3Al and Pt5Al mesoporous catalysts are exceptionally durable and ≈6.3‐ and ≈5.0‐fold more active than the state‐of‐the‐art Pt/C catalyst at 0.90 V, respectively. The high performance makes them promising candidates as cathode nanocatalysts in next‐generation fuel cells.

Copper's oxidation mechanism and purity effects were elucidated by oxidizing 99.99 pct (4N), 99.9999 pct (6N), and floating zone refined (Ͼ99.9999 pct) specimens in 0.1 MPa oxygen at 350 °C to 1050°C. Throughout the temperature range, the oxidation kinetics for all specimens obeys the parabolic oxidation rate law. The Cu 2 O scale grows predominantly, and the rate-determining step is concluded to be outward diffusion of copper atoms in Cu 2 O. The activation energy at high temperatures, where the lattice diffusion predominates, is 173 kJ/mol, but it becomes lower at intermediate temperatures and even lower at low temperatures because of the contribution of the grain boundary diffusion. At high temperatures, oxidation kinetics is almost uninfluenced by purity, but the lattice-diffusion temperature range is wider for higher-purity copper. At intermediate temperatures, copper oxidation is enhanced because trace impurities can impede growth of Cu 2 O grains to facilitate grain boundary diffusion. At low temperatures, grain boundary diffusion is possibly hindered by impurities segregated at grain boundaries.