Electrochemical CO₂ reduction technology could solve the CO₂-induced climate warming by electrochemically converting atmospheric CO₂ back into fuel, essentially recycling it and building a low carbon emission economy. However, the electrochemical CO₂ reduction reaction (CO₂RR) poses a significant challenge due to the highly stable and linear CO₂ molecules, in addition to a proton-coupled multi-electron transfer process. Thus, highly active catalysts, placed on activity bolstering materials, and permeable electrodes are crucial for CO₂RR. Single-atom catalysts (SACs) have recently garnered increasing interest in the electrocatalysis community due to their potentially high mass efficiency and cost benefits (every atom is an active center, resulting in nearly 100% utilization) and adjustable selectivity (higher uniformity of the active sites compared to nanoparticles). However, preserving the accessibility and activity of the SACs inside the electrode poses major materials development and electrode design challenges. A conventional layered structure SAC electrode typically consists of a gas diffusion layer (GDL), a microporous layer (MPL) and a SAC catalyst layer (SACCL), fabricated by using a powder bonding process. However, this process usually encounters issues such as delamination and instability of SACs due to the weak binder-catalyst-support interface. Conversely, the free-standing SAC electrode design has the potential to overcome these issues by eliminating the GDL, MPL, and need of a binder, in contrast to the powder bonding process. This work first reviews the latest developments in experimental and modeling studies of powdered SAC electrode by the traditional powder bonding process. Next, it examines the development towards the free-standing SAC electrode for high-performance electrochemical reduction of CO₂. The synthesis-structure-fabrication-performance relationships of SAC-based materials and associated electrodes are analyzed. Furthermore, the article presents future challenges and perspectives for high-performance SAC electrodes for CO₂RR.

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中文翻译：

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用于二氧化碳减排的独立式单原子催化剂电极

电化学CO ₂还原技术可以通过将大气中的CO ₂电化学转化回燃料，本质上对其进行回收并建立低碳排放经济，从而解决CO ₂引起的气候变暖问题。然而，除了质子耦合的多电子转移过程之外，由于高度稳定和线性的CO ₂分子，电化学CO ₂还原反应（CO ₂ RR）提出了重大挑战。因此，放置在活性支撑材料上的高活性催化剂和可渗透电极对于CO ₂ RR至关重要。单原子催化剂 (SAC) 最近在电催化界引起了越来越多的兴趣，因为它们具有潜在的高质量效率和成本效益（每个原子都是活性中心，导致利用率接近 100%）和可调节的选择性（活性的均匀性更高）与纳米粒子相比的位点）。然而，保持电极内部 SAC 的可接近性和活性给材料开发和电极设计带来了重大挑战。传统的层状结构SAC电极通常由气体扩散层（GDL）、微孔层（MPL）和SAC催化剂层（SACCL）组成，通过粉末粘合工艺制造。然而，由于粘合剂-催化剂-载体界面较弱，该过程通常会遇到分层和SAC不稳定等问题。相反，与粉末粘合工艺相比，独立式 SAC 电极设计有可能通过消除 GDL、MPL 和粘合剂需求来克服这些问题。 本文首先回顾了传统粉末粘合工艺粉末 SAC 电极实验和建模研究的最新进展。接下来，它研究了用于 CO ₂高性能电化学还原的独立式 SAC 电极的发展。分析了 SAC 基材料和相关电极的合成-结构-制造-性能关系。此外，本文还提出了 CO ₂ RR 高性能 SAC 电极的未来挑战和前景。

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