Yuliang Yuan

Renewable electricity‐powered electrocatalysis technologies occupy a central position in clean energy conversion and the pursuit of a net‐zero carbon emission future. Water can serve multiple roles in electrocatalytic reactions, for instance, as a reaction medium, reactant, modifier, promoter, etc. This significantly influences the mass transport, active site, intermediate adsorption and reaction kinetics, ultimately determining the electrocatalytic performance (e.g., activity, selectivity, and stability) as well as device efficiency. As the heart location where electrocatalytic reactions occur, the typical electrical‐double layer is established at a water‐electrode interface. Therefore, the comprehension and regulation of water are crucial topics in electrocatalysis, which encourages us to organize this review. We begin with the fundamental understanding on structure of water and its behavior under electrochemical conditions. Subsequently, we delve into the “water effect” by elucidating specific functions of water in electrocatalysis. Recent advances in manipulating water to enhance electrocatalytic efficiency of representative reactions such as hydrogen evolution/oxidation, oxygen evolution/reduction, CO₂ reduction, N₂ reduction and organic electrosynthesis, are also highlighted. We finally discuss the remaining challenges and future opportunities in this field.

The world's energy landscape is undergoing a significant transformation, driven by the urgent need to address the climate issues and growing sustainable energy demand. Hydrogen can be produced from renewable sources and may play a crucial role in the zero-carbon economy, which is regarded as a promising alternative to fossil fuels. Currently, hydrogen production via water electrolysis still relies on high-purity water, while seawater electrolysis benefits from the abundance of seawater, which can be particularly beneficial for water-scarce countries, and deep-sea applications, such as floating platforms or islands. However, it faces several challenges, such as impurities in seawater, the harsh marine environment, and unpredictable costs. Ongoing research and development efforts are focused on addressing these challenges through innovative solutions, including the design of robust electrocatalysts, the development of smart integrated structures, and the exploration of innovative coupled systems. In this review, the significant progress mentioned above aimed at improving the efficiency of seawater electrolysis is briefly discussed, and the challenges and prospects are provided.

Although anion exchange membrane water electrolyzer (AEMWE) is an emerging device in the green hydrogen production industry, the use of alkaline electrolyte tackles the practicality due to the issues of lowering system efficiency and environmental impacts. State‐of‐the‐art technology using pure water as an electrolyte is advancing to overcome the current challenges of AEMWE. In particular, the development of this technology requires a comprehensive evaluation of techno‐economic aspects, aiming to balance innovation with cost considerations. This involves the critical development of advanced catalysts, membranes, and devices designed for efficiency, as well as assessing their economic viability amidst prevailing technological challenges. This review delves into the timely technical challenges of developing pure water‐fed AEMWE, highlights current progress and research prospects, and suggests opportunities for advancing AEMWE technology. This review also emphasizes the importance of advanced characterization techniques for effective analysis and evaluation in this context.

Electrochemical structural reconstruction of catalysts may generate real active sites that differ from the initial catalyst, but is often ignored. Herein, combining in situ and ex situ techniques, it is identified that the bismuth nanosheets (NS) dotted with large numbers of coordinatively unsaturated pit sites is produced via the in situ structural reconstruction of Bi(OH)₃ NS. Such reconstructed Bi NS shows greatly improved catalytic activity toward CO₂ electroreduction, with a 2.6‐fold increase in current density compared with intact Bi NS, high Faradaic efficiency for HCOO⁻ production (>95%), and an extraordinary turnover frequency of 0.35 s⁻¹ at −0.98 V_RHE. In addition, it delivers industrial‐relevant current density of 325 mA cm⁻² without compromising selectivity in a flow cell. The mechanistic studies demonstrate that these coordinatively unsaturated sites acting as the real active sites favor the stabilization of key intermediate *OCHO, which thus facilitate the reaction kinetics for HCOO⁻ production. This work not only provides a unique perspective on the construction of efficient catalysts for CO₂ electroreduction, but also implies the importance in recognition of structural reconstruction.

Modulating the local coordination structure of metal single-atom catalysts (SACs) is extensively employed to tune the catalytic activity, but rarely involved in regulating the reaction pathway which fundamentally determines the product selectivity. Herein, we report that the product selectivity of electrochemical CO₂ reduction (CO₂RR) on the single-atom indium-N_xC_4−x (1 ≤ x ≤ 4) catalysts could be tuned from formate to CO by varying the carbon and nitrogen occupations in the first coordination sphere. Surprisingly, the optimal In SAC showed great promise for CO production with the maximum Faradic efficiency of 97%, greatly different from the reported In-based catalysts where the formate is the dominant product. Combined experimental verifications and theoretical simulations reveal that the selectivity switch from formate to CO on In SACs originates from active sites shift from indium center to the indium-adjacent carbon atom, where the indium site favors formate formation and the indium-adjacent carbon site prefers the CO pathway. The present work suggests the active sites in metal SACs may shift from the widely accepted metal center to surrounding carbon atoms, thereby offering a new implication to revisit the active sites for metal SACs.

Advancing the development of electrocatalytic CO₂ reduction reaction (CO₂RR) to address the environmental issues caused by excessive consumption of fossil fuels requires rational design of remarkable electrocatalysts, where the identification of active sites and further understanding of structure–performance relationship are the bases. However, the notable dynamic evolution often appears on the catalysts, with typical examples of Cu‐based catalysts, under operating conditions, causing great difficulty in identifying the real active sites and further understanding the correlations between structure and catalytic property. In this context, understanding the dynamic evolution process of catalytically active sites during CO₂RR is of particular importance, which inspires to organize the present review. Herein, the fundamental principles of dynamic evolution in CO₂RR including thermodynamics and kinetics aspects, followed by the introduction of operando techniques employed to probe the evolution under operating conditions are first highlighted. The dynamic evolution behaviors, involving atomic rearrangement and change in chemical state, on typical catalysts are further discussed, with emphasis on the correlations between evolution behaviors and catalytic properties (activity, selectivity, and stability). The emerging CO₂ pulsed electrolysis technique that behaves promise to manipulate the dynamic evolution and future opportunities are finally discussed.

The classical size effect of Pt particles on oxygen reduction reaction (ORR) suggests that the activity and durability would decrease with reducing the particle size, self-limiting the effectiveness in maximizing the Pt utilization efficiency with the particle-size-reduction strategy. Herein, we discover an anomalous size effect based on Pt nanowires (NWs) with tunable diameters, where the monotonically increasing activity and durability for ORR were observed with decreasing the diameter from 2.4 to 1.1 nm. Our results reveal that the dominant role of increased compressive strain induced by decreasing the diameter of NWs in weakening the adsorption and suppressing the Pt dissolution accounts for this anomalous size effect, where the reduced low-coordinated sites on NWs, the intrinsic structural advantage, is the root. Our findings not only expand the knowledge to the classical size effect but also provide new implications to break through the size limit in the design of Pt-based ORR catalysts.