More organizations view PEMFCs as a promising alternative for creating sustainable energy through clean methods. The hydrogen conversion process takes place at both the anode and cathode, where electrochemical reactions carry out complex mechanisms. Reaction efficiency determines the complete fuel cell performance. We will study electrode reactions in PEM fuel cells through anode and cathode analysis, together with an examination of challenges that affect the platinum (Pt) catalyst.
Understanding the Anode Reaction
The main reaction occurring at the anode produces hydrogen oxidation that creates both protons and electrons. The Hydrogen Oxidation Reaction (HOR) occurs on the anode electrocatalyst surface when it happens during operation. The catalytic reaction depends on platinum to transform hydrogen through its main function as catalyst.
During the anode reaction hydrogen molecules decompose while producing protons H⁺ and electrons e⁻ that lead to electricity formation. The Tafel-Volmer pathway together with Heyrovsky-Volmer pathway function as the fundamental driving forces of this reaction.
The Tafel Reaction
At the beginning of hydrogen oxidation the Tafel reaction functions to divide hydrogen molecules (H₂) into hydrogen atoms through platinum surface contact. The platinum surface receives the atoms later losing an electron from each one which produces protons alongside electrons. Both necessary electric power generation elements emerge from this vital reaction.
The Tafel reaction reduces H2 molecules by using two Pt catalysts while producing 2H−PtH_2 + 2Pt \rightarrow 2H-Pt.
Platinum surfaces are symbolized by Pt, and H-Pt denotes hydrogen atoms when adsorbed onto platinum.
The Volmer Reaction
The hydrogen oxidation process requires the Volmer reaction which permits adsorbed hydrogen atoms to interact with water molecules to create protons alongside electrons. The production of protons at the electrolyte depends on this important reaction.
During the Volmer reaction, the reaction takes place as H−Pt+H2O→Pt+H3O++e−H-Pt + H_2O \rightarrow Pt + H_3O^+ + e^-.
The PEM fuel cell requires these hydrogen ion flows to operate because the Volmer Reaction facilitates continuous protons to reach the cathode oxidation reaction site.
The Heyrovsky Reaction
A single-electron oxidation process of hydrogen causes the Heyrovsky reaction to happen. Such an important stage incorporates a dual process that includes hydrogen chemical interaction and the hydrogen oxidation process. The cell works efficiently because this reaction sustains continuous proton and electron movement.
Because of the Heyrovsky reaction, we can define this process as H2+Pt+H2O→H−Pt+H3O++e−H_2 + Pt + H_2O ➡️H-Pt + H_3O^+ + e^-.
The reaction mechanism supports the efficient operation of the entire anode process.
Pt as the Catalyst in the Anode Reaction
Platinum shows universal popularity as a hydrogen oxidation reaction catalyst since it separates hydrogen molecules and liberates protons and electrons efficiently. Platinum runs hydrogen electro-oxidation reactions with extraordinary speed, so it stands as the best possible catalyst material.
The use of highly dispersed Pt/C catalysts makes platinum surfaces larger and boosts reaction speeds. Albeit diminishing the platinum content to 0.05 mg/cm² remains, the fuel cell shows only minimal operational decrease which proves a lower platinum concentration can enhance cell efficiency.
Reducing Pt Loading in PEM Fuel Cells
The research indicates that PEM Fuel Cells function effectively with reduced amounts of platinum.
Researchers focus heavily on decreasing the quantity of platinum used in PEM fuel cells. The expensive nature of platinum coupled with its scarcity makes cost reduction efforts both economical and environmentally beneficial for sustainable fuel cell development. Research results show that better platinum catalyst design along with eco-friendly materials allows PEM fuel cells to maintain their operational stability with diminished platinum amounts.
Understanding the Cathode Reaction
PEM fuel cells use the Oxygen Reduction Reaction (ORR) as their cathode reaction where the electrocatalyst on the cathode performs this reaction. Reduction of oxygen molecules (O₂) at the cathode forms water (H₂O) through proton combination. PEM fuel cells require the ORR to finish their electrochemical cycle by enabling electronic circulation through the external circuit which generates electric energy.
The Four-Electron Reduction of Oxygen
The reaction mechanism of the ORR consists of oxygen molecule reduction with electronic and protonic inputs. The complete reduction of the reaction needs all four electrons to proceed through multiple stages. The ORR acts as a critical factor in determining fuel cell efficiency because reaction speed controls the power output of the cell.
Overpotential in the Cathode Reaction
The reaction demands an excess voltage called overpotential, to proceed past its natural equilibrium state. The theoretical equilibrium potential of the ORR reaches 1.23V yet practical overpotential exceeds 0.25V du ring this reaction. A considerable portion of energy disappears during ORR operations thus decreasing PEM fuel cells’ overall efficiency.
Electrocatalysts in the Cathode Reaction
The development of strong electrocatalysts is needed to lower cathode reaction overpotential and boost its operational efficiency. Platinum (Pt) stands as the preferred material because it demonstrates exceptional catalytic properties when it comes to ORR. The scarcity of platinum coupled with its expensive nature creates an unsustainable situation for its use.
Challenges with Platinum (Pt) for ORR
The best catalyst for ORR exists in platinum, although its expensive nature, along with its restricted availability, hinders PEM fuel cells from reaching broad-scale implementation. Scientists continue research to discover new materials that would perform at least similarly to platinum while eliminating its high expense.
The objective is to decrease the quantity of Pt used in the cathode
Researchers work to cut down platinum usage within PEM fuel cells because of the scarcity of platinum material. Researchers work to create advanced catalysts for fuel cells since developing efficient ways to utilize platinum is still required.
The Future of PEM Fuel Cells
Scientists research PEM fuel cell developments to enhance operational efficiency, together with the affordability of anode and cathode processes. The availability and affordability of fuel cell technology will improve significantly through new catalyst developments that replace platinum.
Conclusion
In conclusion, the electrode reactions in PEM fuel cells —both at the anode and cathode—are critical to the efficiency and performance of the cell. The electrochemical generation of electricity relies on hydrogen oxidation combined with oxygen reduction at the anode and cathode sections.
