The electrochemical reduction of CO₂ (eCO2RR) has emerged as a promising route for carbon-neutral fuel and chemical production, offering a sustainable alternative to fossil-based processes. This article begins with an overview of conventional CO₂ conversion methods, highlighting their limitations and the advantages of electrochemical approaches under ambient conditions. We focus on recent advancements in electrocatalyst development for the eCO2RR, including metal-based, Cu-based, and metal-free catalysts. Metal-based catalysts are categorized by product selectivity (formate, CO, and multicarbon products), emphasizing their structures and practical performance. Cu-based catalysts are discussed in detail due to their unique capability to produce multicarbon products, with emphasis on design strategies, material types, and performance trends. Additionally, we review emerging metal-free catalysts, including their synthesis, mechanisms, and potential applications. This article provides a comparative analysis to guide future research toward efficient, selective, and durable catalysts for CO₂ electroreduction, aiming to accelerate the deployment of carbon capture and utilization technologies.

Proton-conducting solid oxide electrolysis cells (P-SOECs) leverage their low activation energy for proton-conduction to achieve high water electrolysis performance in the intermediate temperature regime (400-600°C). In this sought after temperature zone critical challenges that face high-temperature systems (>700°C) such as balance-of-plant costs, degradation, and oxidation may be alleviated while still retaining favorable reaction kinetics with earth-abundant materials. The electrolyte in P-SOECs plays a vital role in full cell performance and efficiency. P-SOEC electrolytes must have high ionic conductivity, low electronic conductivity, and exceptional durability in high steam atmospheres. Yttrium-doped barium zirconate (BZY) and yttrium/ytterbium co-doped barium cerate zirconate (BZCYYb) are the most widely used P-SOEC electrolyte materials to date. However, practical applications for these materials are in question due to the low protonic conductivity of BZY, poor durability of BZCYYb in high steam environments, and the depressed faradaic efficiencies achieved by P-SOECs utilizing these electrolytes. In this work we show that scandium-doped barium zirconate (BZSc) is a promising electrolyte material to produce P-SOECs with a combination of high performance, efficiency, and durability. Relevant electrolysis current densities were attained below 500°C and long-term durability is demonstrated. Cell architecture and operating conditions are optimized to maximize faradaic efficiency. Our results indicate that high proton concentrations in the electrolyte achieved through high dopant levels can boost performance in barium zirconate-based P-SOECs while preserving unrivalled durability. This work demonstrates the potential for BZSc as an effective P-SOEC electrolyte and we anticipate future studies to further characterize BZSc. Furthermore, this work opens the door for more research into proton conducting materials with dopant levels exceeding 20 mol%.

Protonic ceramic electrochemical cells (PCECs) have emerged as a promising avenue for electrochemically converting the chemical energy in hydrogen into power through fuel cell mode or hydrogen production in electrolysis cell mode, with notable efficiency. The oxygen electrode within PCECs plays a crucial role in facilitating water oxidation and oxygen reduction reactions, pivotal steps for both electrolysis and fuel cell operation, particularly at reduced temperatures. Nevertheless, achieving reproducibility and scalability in electrode material synthesis has presented a significant challenge. In this study, we introduce a scalable synthesis method aimed at enabling the mass production of electrode raw powders along with a better integration approach for large cell fabrication/manufacturing. Additionally, the electrochemical stability of PCECs, particularly under high steam concentration (~50%), can be enhanced by reducing interfacial resistance through optimization of oxygen electrode microstructure, particle size, and catalytic activity. Our developed scalable synthesis approach provides a practical solution for mass-producing oxygen electrodes, thus advancing the efficient fabrication and widespread adoption of PCECs in energy conversion applications.

As one of promising technologies for hydrogen production and valuable chemical production, protonic ceramic electrochemical cells (PCECs) work at relatively low temperatures (400-600^oC), due to high ionic conductivity and low activation energy. However, some undesired structural morphologies and defects presenting in the electrolyte layer during fabrication of PCECs, such as relatively small grain sizes, pinholes, and poor electrolyte/electrode interfaces, presenting detrimental effects on electrochemical performance and durability. PCECs are conventionally fabricated from proton conducting precursor powders, which are usually synthesized by solid state reaction (SSR) method, especially for large quantity fabrication. Thus, the properties and quality of electrolyte precursor powders are crucial for cell performance. Herein, we investigate the influence of fabrication conditions for electrolyte precursors on both manufacturing process and consequential electrochemical performance of PCECs. The present study sheds a light on the discrepancies on the PCEC performance reported in the literature and paves a way for scale-up of PCEC technology.

Protonic ceramic electrochemical cells (PCECs) are promising platforms for efficient energy conversion, hydrogen production, and high-value chemical synthesis at intermediate temperatures. However, large-scale deployment of PCECs remains constrained by the poor sinterability, high fabrication cost, and long processing time associated with state-of-the-art proton-conducting ceramic (PCC) electrolytes. Here, we report a time-efficient, ball-milling-free solid-state reaction approach using nano-sized precursor particles (n-SSR) to synthesize Ba (Zr,Ce,Y,Yb)O _{3− δ} proton-conducting electrolytes with enhanced manufacturability and performance. Compared with the conventional solid-state reaction route using micro-sized precursors ( μ -SSR), the n-SSR process largely shortens powder fabrication time by eliminating ball-milling process while producing fine electrolyte particles (200–600 nm) with superior sintering activity. As a result, PCECs fabricated with n-SSR electrolytes exhibit lower densification temperature and markedly improved electrochemical performance, delivering a 32% higher peak power density in fuel cell mode and a 40% higher electrolysis current density at 600 °C, primarily due to reduced ohmic resistance. Long-term stability exceeding 500 h without measurable degradation is demonstrated. Importantly, a techno-economic analysis reveals that the n-SSR process reduces total electrolyte fabrication costs by 25%–29% by minimizing comminution, calcination time, and processing complexity. Large-area (5 cm × 5 cm) single-cell fabrication further validates the scalability of this approach. These results establish n-SSR as a practical and generalizable manufacturing strategy for high-performance PCCs, addressing a key bottleneck for the large-scale deployment of protonic ceramic energy technologies.