In industrial electrochemical systems, the Hydrogen Evolution Reaction (HER) is almost inevitably present. Even when hydrogen production is not the system's design objective, HER occurs continuously on the cathode side and participates in the entire electrochemical process as a side reaction.
In electrochemical systems centered on titanium-based electrodes, particularly titanium anodes, HER is typically neither the main reaction nor the target reaction. However, it exerts a substantial influence on the system's cell voltage, energy consumption, interface state, and long-term operational stability. Without a clear understanding of HER mechanisms, engineering practices often misclassify reaction-related issues as material defects, leading to unnecessary design adjustments or procurement misjudgments.
I. Basic Reaction Process of HER: Minimal Chemical Background for Engineering Understanding
From an overall stoichiometric perspective, HER can be expressed through concise reaction equations:
In acidic media:
2H⁺ + 2e⁻ → H₂↑
In alkaline media:
Due to the low concentration of free protons, water molecules serve as the hydrogen source:
2H₂O + 2e⁻ → H₂↑ + 2OH⁻
These equations illustrate HER's end result: electrons are consumed, and hydrogen gas is generated and evolved. However, on real electrode surfaces, HER does not proceed in a single step but through multiple sequential interfacial processes.
II. What Happens on the Electrode Surface: Key Steps from Adsorption to Desorption
At the electrochemical interface, HER typically undergoes two stages:
Stage 1: Electrochemical Adsorption of Hydrogen
Hydrogen species (protons or water molecules) in the electrolyte, after gaining electrons, first adsorb onto active sites on the electrode surface as adsorbed hydrogen (H*). This step determines whether hydrogen can smoothly participate in subsequent reactions.
Stage 2: Hydrogen Gas Generation and Desorption
The adsorbed H* then combines via different pathways and detaches from the surface, forming and evolving as hydrogen gas. This process may involve electron participation or occur purely as a surface chemical reaction.
In engineering operations, HER's rate, required voltage, and gas evolution behavior are directly determined by the relative speed and dominance of these two stages.
III. HER and Overall Cell Voltage Behavior: Why Cathodic Reactions "Raise" System Voltage
Although HER occurs on the cathode side, it directly impacts the system's overall cell voltage from an energy perspective.
When the adsorption or desorption of hydrogen on the electrode surface becomes hindered, a higher driving potential must be applied to the cathode to maintain the same current density. This additional potential requirement manifests as an increase in cell voltage at the system level.
Elevated cell voltage not only increases energy consumption per unit output but also triggers a series of cascading effects:
● Enhanced overall system heating
● Increased burden on thermal management and cooling systems
● Higher thermal stress on seals, support structures, and electrode assemblies during long-term operation
Thus, in titanium anode systems, HER is by no means a negligible "background reaction" but a fundamental process closely linked to system energy efficiency, operating windows, and long-term stability.
IV. Hydrogen Evolution and Bubble Behavior: Direct Engineering Manifestations of HER at the Interface
The most intuitive and observable operational manifestation of HER is the generation and evolution of hydrogen bubbles on the electrode surface.
Hydrogen bubbles are not merely a byproduct exiting the system. During their formation, growth, detachment, and migration, bubbles continuously alter the local state of the electrode-electrolyte interface, including:
● The effective surface area available for reactions
● The distribution of local current density
● Mass transfer conditions and flow states near the interface
When bubbles cover the electrode surface, reactions in certain areas are temporarily blocked, forcing current redistribution. This can manifest as voltage fluctuations, unstable current, or changes in apparent efficiency.
Without an understanding of HER mechanisms, these phenomena are often misattributed in engineering practice to inadequate titanium anode performance, unreasonable structural design, or even simply "anode instability." In reality, in many cases, these behaviors are normal electrochemical responses of HER under specific operating conditions.
V. When Abnormalities Occur: How to Diagnose Based on HER Mechanisms
In the actual operation of titanium-based electrode systems, common phenomena include:
● Gradual increase in cell voltage over time
● Significant changes in hydrogen evolution behavior
● Phased fluctuations in energy efficiency or current efficiency
These phenomena do not necessarily indicate electrode material failure. A considerable number of issues stem from changes in HER interfacial
behavior caused by altered operating conditions. For example:
● When hydrogen desorption is impaired, bubbles tend to linger on the surface
● Changes in the interface state increase the system's sensitivity to voltage and current distribution
In such cases, a reasonable engineering diagnosis sequence should be:
1.First analyze whether HER is constrained under the current operating conditions
2.Then evaluate the impact of hydrogen bubble behavior on the interface and current distribution
3.Finally determine if genuine material or structural defects exist
This mechanism-driven diagnostic approach can significantly reduce the risk of misjudgment.
VI. Why HER Knowledge Is Particularly Important for Industrial Procurers
For industrial procurers, HER is not merely a theoretical model in electrochemistry textbooks but a critical tool for understanding and interpreting system operating states.
Changes in cell voltage, hydrogen evolution patterns, and energy efficiency fluctuations often reflect shifts in HER kinetic conditions rather than simple "equipment quality" or "material superiority." Being able to interpret these signals from a mechanistic perspective helps accurately distinguish between:
● Behavioral changes under normal operating conditions
● Problems caused by parameter adjustments or operating condition deviations
● Abnormal states requiring genuine engineering intervention
VII. HER-Related Abnormalities → Potential Causes → Engineering Response Strategies
(A Diagnostic Guide for Titanium-Based Electrode System Operation)
In industrial electrochemical systems using titanium-based electrodes (especially titanium anodes), HER persists as a side reaction. In most cases, it does not cause issues; however, when operating conditions change or exceed reasonable windows, HER's interfacial behavior may be amplified, leading to a range of "apparently abnormal" operational phenomena.
The purpose of this section is not to simplify blame materials but to help engineers and procurers clarify the engineering logic of "phenomenon → cause → response" based on HER mechanisms.
1. Gradual Increase or Amplified Fluctuations in Cell Voltage
🔍 Common Manifestations
Cell voltage gradually rises over time at constant current density
Periodic or irregular voltage fluctuations
Moderate but persistent increases
🧠 Potential HER-Related Causes
Constrained HER kinetics on the cathode side, requiring higher driving potential
Slower hydrogen adsorption or desorption on the electrode surface
Prolonged bubble retention at the interface, causing local reaction blockages
These factors increase cathode overpotential, ultimately reflecting in higher overall cell voltage.
🔧 Operational Adjustment Strategies
Review whether operating parameters (current density, temperature, electrolyte state) have changed
Observe if bubble evolution is denser or less likely to detach than before
Prioritize evaluating reaction mechanism or operating condition changes over directly attributing to material degradation
2. Abnormal Hydrogen Evolution (Larger Bubbles, Prolonged Attachment)
🔍 Common Manifestations
Significantly larger hydrogen bubbles
Extended bubble retention on the electrode surface
Uneven evolution with dense bubbles in local areas
🧠 Potential HER-Related Causes
Impaired hydrogen desorption, leading to accumulated adsorbed hydrogen on the surface
Changes in the interface state affecting bubble nucleation and detachment
Uneven local current density causing concentrated HER
These phenomena are typically related to the desorption stage of HER and do not necessarily indicate electrode material problems.
🔧 Operational Adjustment Strategies
Determine if bubble behavior coincides with changes in operating conditions
Check for variations in local flow fields or mass transfer conditions
Treat bubble behavior as an interfacial reaction signal rather than direct evidence of material failure
3. Phased Decline in Current Efficiency or Energy Efficiency
🔍 Common Manifestations
Reduced effective product output per unit of electricity
Increased system energy consumption without obvious structural damage
Stage-dependent or condition-correlated changes
🧠 Potential HER-Related Causes
HER consumes more electrons, increasing its relative contribution
HER rate outpaces the main reaction, causing current diversion
Interface changes favor HER occurrence
In such cases, HER transitions from a "background side reaction" to a more dominant process, affecting overall system efficiency.
🔧 Operational Adjustment Strategies
Analyze if current operating conditions favor HER (e.g., excessively high driving potential)
Evaluate whether optimizing operating parameters can restore the main reaction's dominance
Avoid forcing production capacity by simply "increasing voltage"
4. Unstable Current Distribution or Local Overheating
🔍 Common Manifestations
Localized temperature elevation
Uneven current distribution with "hot spots"
High sensitivity to minor parameter changes
🧠 Potential HER-Related Causes
Bubble coverage altering local reaction areas
Current redistribution around bubble-blocked regions
Interface disturbances from HER amplifying local discrepancies
These issues are often the result of superimposed interfacial phenomena rather than single-point failures.
🔧 Operational Adjustment Strategies
Analyze the problem at the "interfacial behavior + reaction mechanism" level
Integrate observations of gas behavior and temperature distribution for comprehensive judgment
Avoid isolated interventions targeting "local abnormalities"
5. Common Misjudgments and Engineering Reminders
In practical engineering and procurement, HER-related phenomena are often misclassified as:
❌ Insufficient titanium anode material performance
❌ Unstable manufacturing quality
❌ Defective structural design
However, in numerous engineering cases, these manifestations are more commonly caused by:Changes in HER interfacial behavior due to altered operating conditions
6. Engineering Path from "Observing Phenomena" to "Making Correct Judgments"
When abnormalities occur in titanium-based electrode systems, a more reliable diagnostic sequence is:
1.Identify if the phenomenon is related to HER
2.Analyze if current operating conditions amplify HER behavior
3.Evaluate the impact of gas behavior on the interface and current distribution
4.Finally assess potential material or structural issues
This mechanism-driven approach enhances the controllability and predictability of system operations.
From Reaction Mechanisms to Reliable Engineering and Procurement Decisions
Mature and robust engineering and procurement decisions should not be based solely on parameter sheets, technical specifications, or single test results. More importantly, they require an understanding of the reaction mechanisms underlying these indicators and their potential behavioral patterns under real operating conditions.
When decisions are grounded in a comprehensive understanding of HER and its engineering impacts, the selected titanium-based electrode system is more likely to demonstrate stability, consistency, and predictability in practical applications-critical factors for long-term continuous operation.
Conclusion: HER Is a Fundamental Reaction That Must Be Correctly Understood in Titanium Anode Systems
HER is neither the main reaction in titanium anode systems nor should it be simply labeled a "problematic" or "side reaction." In most industrial applications, it exists as a side reaction and exerts tangible impacts on system performance under specific operating conditions.
Only through a thorough understanding of HER's basic chemical processes, interfacial mechanisms, and engineering manifestations can the performance boundaries, operational stability, and service life of titanium-based electrode systems be truly comprehended and controlled.