The selection of oxide materials for catalyzing the oxygen evolution reaction in acid-based electrolyzers must be guided by the proper balance between activity, stability and conductivity—a challenging mission of great importance for delivering affordable and environmentally friendly hydrogen. Here we report that the highly conductive nanoporous architecture of an iridium oxide shell on a metallic iridium core, formed through the fast dealloying of osmium from an Ir₂₅Os₇₅ alloy, exhibits an exceptional balance between oxygen evolution activity and stability as quantified by the activity-stability factor. On the basis of this metric, the nanoporous Ir/IrO₂ morphology of dealloyed Ir₂₅Os₇₅ shows a factor of ~30 improvement in activity-stability factor relative to conventional iridium-based oxide materials, and an ~8 times improvement over dealloyed Ir₂₅Os₇₅ nanoparticles due to optimized stability and conductivity, respectively. We propose that the activity-stability factor is a key “metric” for determining the technological relevance of oxide-based anodic water electrolyzer catalysts.

As climate change becomes increasingly evident, reducing greenhouse gases including CO₂ has received growing attention. Because CO₂ is thermodynamically very stable, its conversion into value-added chemicals such as CO, CH₄, or C₂H₄ is difficult, and developing efficient catalysts for CO₂ conversion is important work. CO₂ can be converted using the gas-phase reaction, liquid-phase reaction, photocatalytic reaction, or electrochemical reaction. The gas-phase reaction includes the dry reforming of methane using CO₂ and CH₄, or CO₂ hydrogenation using CO₂ and H₂. The liquid-phase reaction includes formic acid formation from pressurized CO₂ and H₂ in aqueous solution. The photocatalytic reaction is commonly known as artificial photo-synthesis, and produces chemicals from CO₂ and H₂O under light irradiation. The electrochemical reaction can produce chemicals from CO₂ and H₂O using electricity. In this review, the heterogeneous catalysts used for the gas-phase reaction or electrochemical reactions are discussed, because the liquid-phase reaction and photocatalytic reaction typically suffer from low productivity and poor durability. Because the gas-phase reaction requires a high reaction temperature of > 600 °C, obtaining good durability is important. The strategies for designing catalysts with good activity and durability will be introduced. Various materials have been tested for electrochemical conversion, and it has been shown that specific metals can produce specific products, such as Au or Ag for CO, Sn or Bi for formate, Cu for C₂H₄. Other unconventional catalysts for electrochemical CO₂ reduction are also introduced.

Minimizing the use of Pt catalysts in proton exchange membrane fuel cells (PEMFCs) is important, considering its high price and scarcity. Herein, we demonstrate novel catalysts for PEMFCs with exceptionally high mass activity and durability, in which block copolymer-based carbon supports are loaded with an ultra-small amount of Pt. The mass activity measured after 30 000 cycles of single cell tests was 0.81 A mg_Pt ⁻¹ at 0.9 V, which is the highest performance reported to date. The newly developed catalyst yielded nearly the same power density as that of the commercial Pt/C, even with 1/20 of the Pt usage. The carbon supports were prepared by carbonizing crosslinked domains of block copolymer particles selectively, resulting in mesoporous carbon particles with ∼25 nm pores. When Pt was deposited, thin carbon shells were formed encapsulating PtFe nanoparticles, catalyzing the oxygen reduction reaction efficiently with high durability.