The pH effect on electrochemical reactions is a critical factor influencing proton-coupled electron transfer (PCET) processes. This review summarizes recent research on how pH affects various electrochemical reactions, including the hydrogen evolution reaction (HER)/hydrogen oxidation reaction (HOR), oxygen reduction reaction (ORR)/oxygen evolution reaction (OER), and carbon dioxide reduction reaction (CO₂RR). A bibliometric analysis of 1007 articles from 1985 to 2023 reveals that HER and ORR are the most studied reactions, with significant research activity increasing since 2018. The analysis also highlights the importance of catalyst design and modification, with studies focusing on noble metals, single-atom catalysts, and carbon-based materials. The Sabatier principle and density functional theory (DFT) have been used to understand the thermodynamics and kinetics of these reactions. pH influences electrochemical processes through mass transport, electrochemical double layer (EDL) structure, and surface adsorption energy. The review discusses the mechanisms governing these reactions, emphasizing the role of pH in both proton and electron transfer. Challenges in understanding pH effects include the origin of the pH dependence in reaction rates and the interplay between various factors such as proton donor changes, surface hydrogen binding energy, EDL interface water network connectivity, and adsorbent dipole field interactions. Future research should focus on clarifying these mechanisms and exploring new directions, such as the pH effect on CO₂RR. The review concludes that the design and optimization of catalysts remain key areas of research, with a focus on improving reaction efficiency and selectivity.The pH effect on electrochemical reactions is a critical factor influencing proton-coupled electron transfer (PCET) processes. This review summarizes recent research on how pH affects various electrochemical reactions, including the hydrogen evolution reaction (HER)/hydrogen oxidation reaction (HOR), oxygen reduction reaction (ORR)/oxygen evolution reaction (OER), and carbon dioxide reduction reaction (CO₂RR). A bibliometric analysis of 1007 articles from 1985 to 2023 reveals that HER and ORR are the most studied reactions, with significant research activity increasing since 2018. The analysis also highlights the importance of catalyst design and modification, with studies focusing on noble metals, single-atom catalysts, and carbon-based materials. The Sabatier principle and density functional theory (DFT) have been used to understand the thermodynamics and kinetics of these reactions. pH influences electrochemical processes through mass transport, electrochemical double layer (EDL) structure, and surface adsorption energy. The review discusses the mechanisms governing these reactions, emphasizing the role of pH in both proton and electron transfer. Challenges in understanding pH effects include the origin of the pH dependence in reaction rates and the interplay between various factors such as proton donor changes, surface hydrogen binding energy, EDL interface water network connectivity, and adsorbent dipole field interactions. Future research should focus on clarifying these mechanisms and exploring new directions, such as the pH effect on CO₂RR. The review concludes that the design and optimization of catalysts remain key areas of research, with a focus on improving reaction efficiency and selectivity.