Laser-Induced Pd-PdO/rGO Catalysts for Enhanced Electrocatalytic Conversion of Nitrate into Ammonia

Electrochemical reduction of nitrate to ammonia (eNO3RR) is proposed as a sustainable solution for high-rate ammonia synthesis under ambient conditions. The complex, multistep eNO3RR mechanism necessitates the use of a catalyst for the complete conversion of nitrate to ammonia. Our research focuses on developing a novel Pd-PdO doped in a reduced graphene oxide (rGO) composite catalyst synthesized via a laser-assisted one-step technique. This catalyst demonstrates dual functionality: palladium (Pd) boosts hydrogen adsorption, while its oxide (PdO) demonstrates considerable nitrogen adsorption affinity and exhibits a maximum ammonia yield of 5456.4 ± 453.4 μg/h/cm2 at −0.6 V vs reversible hydrogen electrode (RHE), with significant yields for nitrite and hydroxylamine under ambient conditions in a nitrate-containing alkaline electrolyte. At a lower potential of −0.1 V, the catalyst exhibited a minimal hydrogen evolution reaction of 3.1 ± 2.2% while achieving high ammonia selectivity (74.9 ± 4.4%), with the balance for nitrite and hydroxylamine. Additionally, the catalyst’s stability and activity can be regenerated through the electrooxidation of Pd.


Calculation of standard Gibbs energy
As we detected hydroxylamine in the electrolyte, the possible reaction pathway is proposed below in equations 1 to 5.

Standard Gibbs Free Energy of Formation (ΔG o f)
The standard Gibbs free energies of formation at 25°C (298 K) 22 for the species involved:

Figure S15 .
Figure S15.(a) Online mass spectrum recorded during the degassing at 200 °C, nitrogen

Figure S3 .
Figure S3.(a) Scanning electron microscopic (SEM) images of rGO in different

Figure S15 .
Figure S15.(a) Online mass spectrum recorded during the degassing at 200 °C, nitrogen

Table S1 .
Comparison of ammonia concentration analyzed by ammonia ion selective electrode and Indophenol method.

Table S2 .
Comparison of H-Pd/rGO composite catalyst performance with that of previously reported catalysts.

Table S1 .
Comparison of ammonia concentration analyzed by ammonia ion selective electrode and Indophenol method.

Table S2 .
Comparison of H-Pd/rGO composite catalyst performance with that of previously reported catalysts.