Bipolar Electrochemistry for Concurrently Evaluating the Stability of Anode and Cathode Electrocatalysts and the Overall Cell Performance during Long-Term Water Electrolysis

Electrochemical efficiency and stability are among the most important characteristics of electrocatalysts. These parameters are usually evaluated separately for the anodic and cathodic half-cell reactions in a three-electrode system or by measuring the overall cell voltage between the anode and cathode as a function of current or time. Here, we demonstrate how bipolar electrochemistry can be exploited to evaluate the efficiency of electrocatalysts for full electrochemical water splitting while simultaneously and independently monitoring the individual performance and stability of the half-cell electrocatalysts. Using a closed bipolar electrochemistry setup, all important parameters such as overvoltage, half-cell potential, and catalyst stability can be derived from a single galvanostatic experiment. In the proposed experiment, none of the half-reactions is limiting on the other, making it possible to precisely monitor the contribution of the individual half-cell reactions on the durability of the cell performance. The proposed approach was successfully employed to investigate the long-term performance of a bifunctional water splitting catalyst, specifically amorphous cobalt boride (Co₂B), and the durability of the electrocatalyst at the anode and cathode during water electrolysis. Additionally, by periodically alternating the polarization applied to the bipolar electrode (BE) modified with a bifunctional oxygen electrocatalyst, it was possible to explicitly follow the contributions of the oxygen reduction (ORR) and the oxygen evolution (OER) half-reactions on the overall long-term durability of the bifunctional OER/ORR electrocatalyst

Rapid and Surfactant-Free Synthesis of Bimetallic Pt–Cu Nanoparticles Simply via Ultrasound-Assisted Redox Replacement

The synthesis of bimetallic nanoparticles (NPs) with well-defined morphology and a size of <5 nm remains an ongoing challenge. Here, we developed a facile and efficient approach to the design of bimetallic nanostructures by the galvanic replacement reaction facilitated by high-intensity ultrasound (100 W, 20 kHz) at low temperatures. As a model system, Pt–Cu NPs deposited on nitrogen-doped carbon nanotubes (NCNTs) were synthesized and characterized by spectroscopic and microscopic techniques. Transmission electron microscopy (TEM) inspection shows that the mean diameter of Pt–Cu NPs can be as low as ≈2.8 nm, regardless of the much larger initial Cu particle size, and that a significant increase in particle number density by a factor of 35 had occurred during the replacement process. The concentration of the Pt precursor solution as well as of the size of the seed particles were found to control the size of the bimetallic NPs. Energy dispersive X-ray spectroscopy performed in the scanning TEM mode confirmed the alloyed nature of the Pt–Cu NPs. Electrochemical oxygen reduction measurements demonstrated that the resulting Pt–Cu/NCNT catalysts exhibit an approximately 2-fold enhancement in both mass- and area-related activities compared with a commercial Pt/C catalyst

Metallic NiPS₃@NiOOH Core–Shell Heterostructures as Highly Efficient and Stable Electrocatalyst for the Oxygen Evolution Reaction

We report metallic NiPS₃@NiOOH core–shell heterostructures as an efficient and durable electrocatalyst for the oxygen evolution reaction, exhibiting a low onset potential of 1.48 V (vs RHE) and stable performance for over 160 h. The atomically thin NiPS₃ nanosheets are obtained by exfoliation of bulk NiPS₃ in the presence of an ionic surfactant. The OER mechanism was studied by a combination of SECM, in situ Raman spectroscopy, SEM, and XPS measurements, which enabled direct observation of the formation of a NiPS₃@NiOOH core–shell heterostructure at the electrode interface. Hence, the active form of the catalyst is represented as NiPS₃@NiOOH core–shell structure. Moreover, DFT calculations indicate an intrinsic metallic character of the NiPS₃ nanosheets with densities of states (DOS) similar to the bulk material. The high OER activity of the NiPS₃ nanosheets is attributed to a high density of accessible active metallic-edge and defect sites due to structural disorder, a unique NiPS₃@NiOOH core–shell heterostructure, where the presence of P and S modulates the surface electronic structure of Ni in NiPS₃, thus providing excellent conductive pathway for efficient electron-transport to the NiOOH shell. These findings suggest that good size control during liquid exfoliation may be advantageously used for the formation of electrically conductive NiPS₃@NiOOH core–shell electrode materials for the electrochemical water oxidation