pH plays a pivotal role in influencing various aspects of proton-coupled electron transfer (PCET) reactions in electrochemical systems. These reactions are affected by pH in terms of mass transport, electrochemical double layer (EDL) structure, and surface adsorption energy, all of which impact the overall electrochemical processes. This review article aims to provide a comprehensive understanding of the research progress made in elucidating the effects of pH on different electrochemical reactions, the hydrogen evolution reaction/hydrogen oxidation reaction (HER/HOR), oxygen reduction reaction/oxygen evolution reaction (ORR/OER), and carbon dioxide reduction reaction ( CO2RR). To embark on this endeavor, we have conducted a bibliometric analysis to clearly outline of the research trends and advancements in the field concerning the pH effects. Subsequently, we present a systematic overview of the mechanisms governing these reactions, with a special focus on pH’s influence on both the proton and electron aspects. We conclude by discussing the current challenges in this area and suggesting future research avenues that could further our understanding of pH's role in electrochemical reactions.

Mechanism in pH effects of electrochemical reactions: a mini-review
    Abstract
        Graphical abstract
    1 Introduction
    2 Influence on protons
        2.1 Local pH variation and mass transfer effects
        2.2 Surface hydrogen binding energy (HBE) and hydroxyl binding energy (OHBE)
        2.3 Variations in proton donors
        2.4 Hydrogen bond networking
        2.5 Proton affinity
        2.6 Protonation of nitrogen-doped carbon-based catalysts
    3 Influence on electrons
        3.1 Electron transfer
            3.1.1 Inner-sphereouter-sphere electron transfer (ISETOSET) mechanisms
            3.1.2 Number of electron transfer
        3.2 Electric field effect
            3.2.1 Interaction of adsorbate dipole fields
            3.2.2 Adsorption of anions
            3.2.3 Interface water reorganization
            3.2.4 Electrode potential
    4 Computational study
    5 Conclusions and perspectives
    Acknowledgements 
    References

• Sibei Liu(State Key Laboratory of Urban Water Resource and Environment, School of Environment, Harbin Institute of Technology, Harbin 150090, People’s Republic of China)
• Zhuowen Wang(State Key Laboratory of Urban Water Resource and Environment, School of Environment, Harbin Institute of Technology, Harbin 150090, People’s Republic of China)
• Shan Qiu(State Key Laboratory of Urban Water Resource and Environment, School of Environment, Harbin Institute of Technology, Harbin 150090, People’s Republic of China)
• Fengxia Deng(State Key Laboratory of Urban Water Resource and Environment, School of Environment, Harbin Institute of Technology, Harbin 150090, People’s Republic of China) Corresponding author