电催化硝酸盐还原合成氨（NitRR）是一条将环境污染治理与高附加值化学品生产相结合的绿色可持续路径。然而，其活性与选择性受限于瞬态中间体——活性氢（*H）的生成、消耗与动态平衡。实现活性氢的精准调控，必须首先依赖于先进的原位电化学表征技术对其行为进行全面解析。尽管已有综述从调控策略、原位表征总览等角度进行论述，但系统评述如何合理选用原位电化学技术对NitRR中的*H进行专门表征，并清晰界定各技术的“检测对象、定量精度与应用边界”的工作仍属空白。本文旨在填补这一方法学空缺，系统梳理了用于解析NitRR中*H行为的原位电化学表征技术，包括原位谱学技术、原位电化学方法和扫描电化学显微镜技术。基于这些先进表征技术，在该综述中，我们重点构建了一个针对NitRR过程中*H表征的“问题导向”的多层次方法学框架。通过阐述这些技术的原理、应用实例与适用范围，旨在为后续活性氢研究中的表征技术选择提供可靠依据，从而深化对NitRR微观机制的理解。此外，还探讨了未来的研究方向和发展趋势，为推动高效、高选择性绿色氨合成技术的发展提供了相关指导。

Electrocatalytic nitrate reduction to ammonia (NitRR) represents a sustainable pathway that integrates environmental remediation with the production of high-value ammonia. However, the activity and selectivity of this process are limited by the generation, consumption, and dynamic equilibrium of the key transient intermediate—active hydrogen (*H). Precise modulation of *H necessitates a comprehensive understanding of its behavior, which relies fundamentally on advanced in situ electrochemical characterization techniques. However, a systematic review dedicated to the rational selection and application of in situ electrochemical techniques for the specific characterization of *H in NitRR, with clear definitions of each technique's "detectable targets, quantitative accuracy, and application boundaries" remains absent. This review aims to fill this methodological gap by systematically summarizing in situ electrochemical techniques for probing *H behavior in NitRR, including in situ spectroscopic techniques, in situ electrochemical methods, and scanning electrochemical microscopy. We construct a problem-oriented hierarchical methodological framework tailored for *H characterization in NitRR. By detailing the principles, representative applications, and limitations of these techniques, this review provides a reliable guide for selecting appropriate characterization methods in future *H research, thereby deepening the mechanistic understanding of NitRR. Additionally, future research directions and development trends are discussed, offering insights to advance efficient and selective green ammonia synthesis technologies.