Search for: All records

The hydrogen peroxide (H₂O₂) generation via the electrochemical oxygen reduction reaction (ORR) under ambient conditions is emerging as an alternative and green strategy to the traditional energy‐intensive anthraquinone process and unsafe direct synthesis using H₂and O₂. It enables on‐site and decentralized H₂O₂production using air and renewable electricity for various applications. Currently, atomically dispersed single metal site catalysts have emerged as the most promising platinum group metal (PGM)‐free electrocatalysts for the ORR. Further tuning their central metal sites, coordination environments, and local structures can be highly active and selective for H₂O₂production via the 2e⁻ORR. Herein, recent methodologies and achievements on developing single metal site catalysts for selective O₂to H₂O₂reduction are summarized. Combined with theoretical computation and advanced characterization, a structure–property correlation to guide rational catalyst design with a favorable 2e⁻ORR process is aimed to provide. Due to the oxidative nature of H₂O₂and the derived free radicals, catalyst stability and effective solutions to improve catalyst tolerance to H₂O₂are emphasized. Transferring intrinsic catalyst properties to electrode performance for viable applications always remains a grand challenge. The key performance metrics and knowledge during the electrolyzer development are, therefore, highlighted.

A major challenge in the electrochemical oxidation of hydrocarbons is understanding the formation of intermediate species, some of which continue to react, while others are non‐reactive or poisonous species that block adsorption of further reactants. Herein we investigate the identity and behavior of adsorbates formed during partial oxidation of propene. We employ two techniques: Electrochemistry‐Mass Spectrometry (EC‐MS) and Attenuated Total Reflection Infrared Spectroscopy (ATR‐FTIR). In both cases, we use CO as a probe molecule, to perturb the ad‐layer of propene intermediates. In the EC‐MS experiments, propene and its intermediates were quantified by triggering their desorption via displacement with CO. We show evidence for at least two distinct classes of propene adsorbates, via CO displacement and electrochemical stripping. A redshift in the ν(C−O) mode was observed, during IR spectroscopy, reflecting the chemical environment arising from strongly bound propene intermediates.

Understanding the differences between reactions driven by elevated temperature or electric potential remains challenging, largely due to materials incompatibilities between thermal catalytic and electrocatalytic environments. We show that Ni, N‐doped carbon (NiPACN), an electrocatalyst for the reduction of CO₂to CO (CO₂R), can also selectively catalyze thermal CO₂to CO via the reverse water gas shift (RWGS) representing a direct analogy between catalytic phenomena across the two reaction environments. Advanced characterization techniques reveal that NiPACN likely facilitates RWGS on dispersed Ni sites in agreement with CO₂R active site studies. Finally, we construct a generalized reaction driving‐force that includes temperature and potential and suggest that NiPACN could facilitate faster kinetics in CO₂R relative to RWGS due to lower intrinsic barriers. This report motivates further studies that quantitatively link catalytic phenomena across disparate reaction environments.

Understanding the differences between reactions driven by elevated temperature or electric potential remains challenging, largely due to materials incompatibilities between thermal catalytic and electrocatalytic environments. We show that Ni, N‐doped carbon (NiPACN), an electrocatalyst for the reduction of CO₂to CO (CO₂R), can also selectively catalyze thermal CO₂to CO via the reverse water gas shift (RWGS) representing a direct analogy between catalytic phenomena across the two reaction environments. Advanced characterization techniques reveal that NiPACN likely facilitates RWGS on dispersed Ni sites in agreement with CO₂R active site studies. Finally, we construct a generalized reaction driving‐force that includes temperature and potential and suggest that NiPACN could facilitate faster kinetics in CO₂R relative to RWGS due to lower intrinsic barriers. This report motivates further studies that quantitatively link catalytic phenomena across disparate reaction environments.

Designing acid‐stable oxygen evolution reaction electrocatalysts is key to developing sustainable energy technologies such as polymer electrolyte membrane electrolyzers but has proven challenging due to the high applied anodic potentials and corrosive electrolyte. This work showcases advanced nanoscale microscopy techniques supported by complementary structural and chemical characterization to develop a fundamental understanding of stability in promising SrIrO₃thin film electrocatalyst materials. Cross‐sectional high‐resolution transmission electron microscopy illustrates atomic‐scale bulk and surface structure, while secondary ion mass spectrometry imaging using a helium ion microscope provides the nanoscale lateral elemental distribution at the surface. After accelerated degradation tests under anodic potential, the SrIrO₃film thins and roughens, but the lateral distribution of Sr and Ir remains homogeneous. A layer‐wise dissolution mechanism is hypothesized, wherein anodic potential causes the IrO_x‐rich surface to dissolve and be regenerated by Sr leaching. The characterization approaches utilized herein and mechanistic insights into SrIrO₃are translatable to a wide range of catalyst systems.

Ni,N‐doped carbon catalysts have shown promising catalytic performance for CO₂electroreduction (CO₂R) to CO; this activity has often been attributed to the presence of nitrogen‐coordinated, single Ni atom active sites. However, experimentally confirming Ni−N bonding and correlating CO₂reduction (CO₂R) activity to these species has remained a fundamental challenge. We synthesized polyacrylonitrile‐derived Ni,N‐doped carbon electrocatalysts (Ni‐PACN) with a range of pyrolysis temperatures and Ni loadings and correlated their electrochemical activity with extensive physiochemical characterization to rigorously address the origin of activity in these materials. We found that the CO₂R to CO partial current density increased with increased Ni content before plateauing at 2 wt % which suggests a dispersed Ni active site. These dispersed active sites were investigated by hard and soft X‐ray spectroscopy, which revealed that pyrrolic nitrogen ligands selectively bind Ni atoms in a distorted square‐planar geometry that strongly resembles the active sites of molecular metal–porphyrin catalysts.

Ni,N‐doped carbon catalysts have shown promising catalytic performance for CO₂electroreduction (CO₂R) to CO; this activity has often been attributed to the presence of nitrogen‐coordinated, single Ni atom active sites. However, experimentally confirming Ni−N bonding and correlating CO₂reduction (CO₂R) activity to these species has remained a fundamental challenge. We synthesized polyacrylonitrile‐derived Ni,N‐doped carbon electrocatalysts (Ni‐PACN) with a range of pyrolysis temperatures and Ni loadings and correlated their electrochemical activity with extensive physiochemical characterization to rigorously address the origin of activity in these materials. We found that the CO₂R to CO partial current density increased with increased Ni content before plateauing at 2 wt % which suggests a dispersed Ni active site. These dispersed active sites were investigated by hard and soft X‐ray spectroscopy, which revealed that pyrrolic nitrogen ligands selectively bind Ni atoms in a distorted square‐planar geometry that strongly resembles the active sites of molecular metal–porphyrin catalysts.