Mengran Li

Electrolyzer stacks operating under constant dc conditions exhibit reduced performance due to gas bubble accumulation at high loads and increased gas crossover at low loads. Pulsed operation has been proposed to mitigate these effects. However, its practical implementation requires additional power electronic components, introducing cost and efficiency penalties in the power converter. This paper presents a techno-economic framework to evaluate the feasibility of pulsed electrolysis by explicitly accounting for converter-level capital expenditure, operational expenditure, and pulse induced dc-link capacitor aging. Break-even conditions are derived to quantify the minimum reduction in specific energy consumption (SEC) required for pulsed operation to remain cost-competitive with dc operation. A representative case study based on a voltage source converter with minimal topology modification shows that a SEC reduction of 1.35% for high-load and 4.68% for low-load operation is required to offset additional converter costs. These results formulate the feasibility condition of pulsed electrolysis in large-scale applications.

Not all oxygen vacancies are equal, yet metal oxide catalysts are usually designed as if they were. In perovskite fuel-cell cathodes, oxygen vacancies near redox-active and redox-inactive cations play distinct roles in oxygen reduction reaction, ion transport and hydration, but they are usually lumped into one bulk-averaged property. By partially substituting Y with less electronegative Yb in the benchmark BaCo _0.4 Fe _0.4 Zr _0.1 Y _0.1 O _{3− δ} cathode, we reveal that oxygen vacancies near redox-inactive Y/Yb control the vacancy formation near redox-active Co/Fe, and that water in air unlocks such formation. In dry air, the vacancies near Y/Yb can switch off their inductive effects and thus block the formation of vacancies near Co/Fe, whereas in humid air, these vacancies tend to be occupied by water, unlocking the inductive effect and promoting active vacancies. This water-unlocked formation of vacancies near Co/Fe doubles the oxygen reduction reaction activity in humid air and enables a protonic ceramic fuel cell to generate a peak power density of 700 mW cm ^− 2 at 600°C and a stable operation beyond 2,450 h. Our findings suggest that oxygen vacancies are not independent but coupled, with water acting as a switch that turns this coupling into new active sites.

Operation of water electrolysers at elevated temperatures (> 100°C) is a promising method for substantially increasing the efficiency and reduce the cost of green hydrogen production. These efficiency gains are thought to be limited by bubble‐related losses, which manifest as ohmic and mass transport overpotentials. However, there is limited experimental evidence of electrolyzer bubble dynamics in these harsh operating conditions. In this work, we conduct a parametric study of a proton exchange membrane electrolyzer's performance at temperatures up to 120°C and pressures up to 100 bar, while obtaining images of bubble growth and transport. We show that, at elevated temperatures, there is a reduction in the average fraction of flow channel area occupied by bubbles as well as bubble‐related losses, which may be attributed to the decrease in water surface tension as described by classical bubble detachment models. These results underscore the advantages of operating at elevated temperatures, which allows higher‐efficiency green hydrogen production.

Practical electrochemical devices often operate through highly coupled reaction-transport processes whose internal electrochemical states cannot be resolved from the overall cell voltage alone. This blind spot is especially consequential for membrane-electrode assemblies, where standard two-electrode measurements conflate electrode and membrane behaviours, precluding operando separation of catalytic activity, catalyst utilisation, and degradation under working conditions. Here we establish a new operando electrochemical diagnosis framework combining a polyelectrolyte-stabilised silver/ silver-bromide reference electrode and a controlled ionic connection to probe the reactive regions of working devices. This framework is proven effective across acidic, neutral and basic environments for water and CO ₂ electrolysis at current densities up to 500 mA cm ^-2 , and enables direct and independent electrochemical characterisation of catalyst layers under practical conditions. Using this framework, we uncover a hidden transport-driven collapse in catalyst utilisation that causes more than a threefold decrease in catalyst intrinsic activity, and detect catalyst-layer degradation well before any corresponding change becomes apparent in overall cell voltages. These results indicate a pathway towards restoring electrochemical observability and accelerating the development of practical electrochemical energy systems.

Electrochemical CO2 reduction is emerging as a compelling route for renewable energy storage and carbon neutrality. Focus on improving catalyst selectivity and energy efficiency resulted in a surge of catalysis-centered research. The advent of artificial intelligence and high-throughput screening enables parallelized catalyst characterization to accelerate discovery, but their implementation into application-relevant device configurations is challenging. We present a scalable, high-throughput platform based on infrared thermography that preserves realistic electrochemical environments from lab to industrially relevant scales. We demonstrate the spatial and electrochemical homogeneity of a 16-well parallel electrolyzer and validate a combinatorial testing approach using copper-based catalysts with varied loadings and precursor chemistries. The results highlight how activity trends can be rapidly mapped under controlled conditions, while also revealing the limitations of activity-only combinatorial testing, particularly for multiproduct electrochemical applications in complex environments like CO2 electrolysis on Cu. This platform thus provides an efficient pre-screening tool to accelerate catalyst discovery when analyzed appropriately and paired with follow-up single catalyst testing.

Efficient and reliable protonic ceramic fuel cells (PCFCs) necessitate the development of active and durable cathode materials to accelerate the sluggish oxygen reduction reaction (ORR). The most promising PCFC cathode candidates are perovskite‐type structured oxides with mixed oxygen ion, proton, and hole conductivity. However, mixed conductivity often requires materials with alkaline earth elements and the inclusion of these elements in the cathode structure leads to severe degradation in the presence of even small trace amounts of CO ₂ in air. Herein, a new approach is presented to address this challenge by inducing selective in situ phase segregation to engineer the cathode surface and bulk separately. This selective phase segregation is achieved via targeted control of the size mismatch of cations in the perovskite‐type structure, enhancing charge transfer in the bulk while improving CO ₂ resistance at the surface. By co‐incorporating smaller Li ⁺ and larger K ⁺ into the model BaCo _0.4 Fe _0.4 Zr _0.1 Y _0.1 O _3−δ cathode material, it is shown that Li ⁺ segregates to the surface, protecting it from CO ₂ poisoning, while K ⁺ remains in the bulk and accelerates proton transport. Consequently, this in situ restructured cathode can boost the PCFC power output by 30% and improve its CO ₂ tolerance fivefold in the presence of CO ₂ at 600 °C.

Optimizing ORR in PCFC cathodes by balancing proton and oxygen–ion transport.

Protonic ceramic fuel cells (PCFCs) are one of the promising routes to generate power efficiently from various fuels at economically viable temperatures (500–700 °C) due to the use of fast proton conducting oxides as electrolytes. However, the power density and durability of the PCFCs are still limited by their cathodes made from solid metal oxides, which are challenging to address the sluggish oxygen reduction reaction and susceptibility to CO ₂ simultaneously. Here, an alternative approach is reported to address this challenge by developing a new melt‐solid interface through the in situ alkali metal surface segregation and consecutive eutectic formation at perovskite oxide surface at PCFC operating temperatures. This new approach in cathode engineering is successfully demonstrated over lithium and sodium co‐doped BaCo _0.4 Fe _0.4 Zr _0.1 Y _0.1 O _3‐δ perovskite as the model material. These experimental results unveil that the unique in situ formed melt‐solid surface stabilizes the catalytically active phase in bulk and promotes catalytically active sites at surface. The novel engineered melt‐solid interface enhances the stability of the cathode against poisoning in 10% CO ₂ by a factor of 1.5 in a symmetrical cell configuration and by a factor of more than two in PCFC single cells.

Proton exchange membrane water electrolyzers powered by sustainable energy represent a cutting-edge technology for renewable hydrogen generation, while slow anodic oxygen evolution reaction (OER) kinetics still remains a formidable obstacle that necessitates basic comprehension for facilitating electrocatalysts' design. Here, we report a low-iridium complex oxide La_1.2Sr_2.7IrO_7.33 with a unique hexagonal structure consisting of isolated Ir(V)O₆ octahedra and true peroxide O₂^2- groups as a highly active and stable OER electrocatalyst under acidic conditions. Remarkably, La_1.2Sr_2.7IrO_7.33, containing 59 wt % less iridium relative to the benchmark IrO₂, shows about an order of magnitude higher mass activity, 6-folds higher intrinsic activity than the latter, and also surpasses the state-of-the-art Ir-based oxides ever reported. Combined electrochemical, spectroscopic, and density functional theory investigations reveal that La_1.2Sr_2.7IrO_7.33 follows the peroxide-ion participation mechanism under the OER condition, where the inherent peroxide ions with accessible nonbonded oxygen states are responsible for the high OER activity. This discovery offers an innovative strategy for designing advanced catalysts for various catalytic applications.