Nano PdFe Alloy Assembled Film as a Highly Efficient Electrocatalyst toward Hydrogen Evolution in Both Acid and Alkaline Solutions

A series of nano PdFe alloy film electrodes with different ratios were prepared by high-vacuum magnetron sputtering under the action of high-strength magnetic field. Among them, the Pd₃Fe alloy film electrode possesses the best hydrogen evolution activity, which significantly changes the properties of hydrogen adsorption (H_ad) and absorption (H_abs) of Pd. Pd₃Fe is a nanoassembled film, which consists of many tiny nanosheets connected together. The electrochemical surface area of Pd₃Fe electrode is 13 and 7 times that of the Pd/C and Pd electrode, respectively. At the same time, Pd and Fe had formed an alloy structure. The (111) plane of the Pd₃Fe alloy is an obvious positive shift, and the crystal cell is compressed. The electron is transferred from Fe to Pd through XPS analysis, which has proven the electronic relationship between Pd and Fe. DFT calculations have also shown that the ΔG_H* of the Pd₃Fe surface is significantly reduced compared to that of Pd. Reducing the desorption energy of H on the Pd surface is beneficial to improve the electrocatalytic performance. It is noteworthy that the HER activity of Pd₃Fe electrode has exceeded that of Pd/C, Pd, and Pt/C in both 0.5 M H₂SO₄ and 1.0 M KOH. The HER activity of Pd₃Fe electrode is 20, 1.9, and 3.1 times that of Pd/C, Pd, and Pt/C in 1.0 M KOH at −0.2 V. In 0.5 M H₂SO₄, the HER activity of the Pd₃Fe electrode is 6, 3.5, and 1.6 times that of Pd/C, Pd, and Pt/C. The Pd₃Fe film electrode has the most favorable reaction kinetics, with Tafel slopes of 44.7 and 38.7 mV dec^–1 in acidic and alkaline solutions, respectively. The values of the Tafel slope indicate that the mechanism of HER on the Pd₃Fe film electrode is consistent with the Volmer–Heyrovsky pathway, and the Heyrovsky step is a rate-determining step. In this paper, the Pd alloy electrode has exceeded the commercial Pt/C in both acidic and alkaline solutions, which makes it more practical.