Abstract Alkaline water splitting electrocatalysts have been studied for decades; however, many difficulties remain for commercialization, such as sluggish hydrogen evolution reaction (HER) kinetics and poor catalytic stability. Herein, by mimicking the bulk‐heterojunction morphology of conventional organic solar cells, a uniform 10 nm scale nanocube is reported that consists of subnanometer‐scale heterointerfaces between transition metal phosphides and oxides, which serves as an alkaline water splitting electrocatalyst; showing great performance and stability toward HER and oxygen evolution reaction (OER). Interestingly, the nanocube electrocatalyst reveals acid/alkaline independency from the synergistic effect of electrochemical HER (cobalt phosphide) and thermochemical water dissociation (cobalt oxide). From the spray coating process, nanocube electrocatalyst spreads uniformly on large scale (≈6.6 × 5.6 cm 2 ) and is applied to alkaline water electrolyzers, stably delivering 600 mA cm −2 current for >100 h. The photovoltaic‐electrochemical (PV‐EC) system, including silicon PV cells, achieves 11.5% solar‐to‐hydrogen (STH) efficiency stably for >100 h.

Oxygen Evolution Reaction For green hydrogen production, the development of highly active and durable electrode materials that function the under the intermittent power supply of renewable energies is necessary. In article number 2204403, Byung-Hyun Kim, MinJoong Kim, Hyun-Seok Cho, and co-workers propose the rational design of a stable iron-rich nickel-iron layered double hydroxide under dynamic operating conditions for the alkaline oxygen evolution reaction. Its practical feasibility for industrially relevant application in water electroyzers is demonstrated.

Abstract Alkaline water splitting electrocatalysts have been studied for decades; however, many difficulties remain for commercialization, such as sluggish hydrogen evolution reaction (HER) kinetics and poor catalytic stability. Herein, by mimicking the bulk‐heterojunction morphology of conventional organic solar cells, a uniform 10 nm scale nanocube is reported that consists of subnanometer‐scale heterointerfaces between transition metal phosphides and oxides, which serves as an alkaline water splitting electrocatalyst; showing great performance and stability toward HER and oxygen evolution reaction (OER). Interestingly, the nanocube electrocatalyst reveals acid/alkaline independency from the synergistic effect of electrochemical HER (cobalt phosphide) and thermochemical water dissociation (cobalt oxide). From the spray coating process, nanocube electrocatalyst spreads uniformly on large scale (≈6.6 × 5.6 cm 2 ) and is applied to alkaline water electrolyzers, stably delivering 600 mA cm −2 current for >100 h. The photovoltaic‐electrochemical (PV‐EC) system, including silicon PV cells, achieves 11.5% solar‐to‐hydrogen (STH) efficiency stably for >100 h.

Oxygen Evolution Reaction For green hydrogen production, the development of highly active and durable electrode materials that function the under the intermittent power supply of renewable energies is necessary. In article number 2204403, Byung-Hyun Kim, MinJoong Kim, Hyun-Seok Cho, and co-workers propose the rational design of a stable iron-rich nickel-iron layered double hydroxide under dynamic operating conditions for the alkaline oxygen evolution reaction. Its practical feasibility for industrially relevant application in water electroyzers is demonstrated.

A structure-mechanism-performance relationship of metal-free carbon catalysts for outstanding H 2 O 2 production activity and selectivity in alkaline media.

Anion exchange membrane (AEM) water electrolysis (AEMWE) is considered an economical technology for producing green hydrogen energy. However, conventional AEMs comprising polymer backbones with anisotropically aligned cationic pendant groups exhibit unsatisfactory AEMWE performance and durability, limiting their practical implementation. Herein, a facile method for fabricating a durable high-performance AEM via a one-pot monomer-level Menshutkin (m-Men) reaction in a porous mechanical support is proposed. The rationally designed m-Men reaction between multifunctional alkyl halide and tertiary amine monomers creates a highly crosslinked polymer network with isotropically interconnected, high-density cationic groups. This unique structure is favorable for expediting anion conduction within the membrane and enhancing thermochemical robustness. The resultant membrane exhibits unprecedentedly high AEMWE performance with both non-platinum-group metal (PGM) and full-PGM electrodes at 5 wt.% potassium hydroxide and 80 °C, outperforming commercial state-of-the-art AEMs, with ensuring long-term operation. The proposed strategy provides a breakthrough approach for fabricating advanced membranes for various energy applications.

Polymer electrolyte membrane water electrolysis (PEMWE) is hindered by the reliance on expensive iridium-based catalysts. To address this economic challenge, minimizing iridium usage while maintaining performance and durability is imperative. Achieving this goal requires enhanced catalyst utilization through improved electron, ion, and mass transport within the anode. Recent research has increasingly emphasized the development of microporous layers (MPLs) as a key strategy for enhancing the interface between the porous transport layer (PTL) and the catalyst layer (CL). However, standardized methodologies for MPL design and fabrication remain elusive. In this study, a decal-transfer method is presented as an effective method for introducing a uniform, thin MPL at the CL/PTL interface. By varying the MPL properties, including pore size, thickness, and back-layer structure, two-phase transport phenomena are investigated and established guidelines for optimal MPL design. The findings reveal that smaller micrometer-scale pores in the MPL enhance catalyst utilization and strengthen water capillary force, thereby reducing kinetic and transport overpotentials. Moreover, it is demonstrated that, unless the back layer hinders the in-plane mass transport beneath the flow field, its structural configuration has minimal influence on electrolysis performance. These results underscore the importance of the CL/PTL interface in determining the overall efficiency of PEMWE systems.

Anion Exchange Membrane Water Electrolysis In article number 2405468, EunAe Cho, Chanwon Jung, MinJoong Kim, and co-workers demonstrate that the ternary compositions of Fe-Co-Ni electrocatalysts correlate between the degree of crystallinity and oxygen evolution activity (OER). By analyzing 21 series of ternary compositions, the Fe-Co3-Ni electrocatalysts, which possess optimal composition and structural disorder, exhibit enhanced OER activity and stability, contributing to sustainable green hydrogen production.