Potential-Rate Correlations of Supported Palladium-Based Catalysts for Aqueous Formic Acid Dehydrogenation.

Aqueous formic acid dehydrogenation (FAD) is a crucial process for hydrogen production, as hydrogen is a clean energy carrier. During this process, formic acid converts into hydrogen and carbon dioxide over a catalyst. Pd-based catalysts have exhibited significant potential in FAD due to their high activity and selectivity. In this study, we investigated aqueous thermal FAD in a mixture of formic acid and sodium formate using electrochemical open-circuit potential (OCP) measurement by loading the catalysts onto a conductive substrate as a working electrode. By varying the reaction conditions such as the concentration of reactants and modifying Pd with Ag, different FAD rates were obtained. Consequently, we revealed the correlation between the catalyst OCP and FAD rate; superior FAD rates reflected a more negative catalyst OCP. Furthermore, deactivation was observed across all catalysts during FAD, with a concurrent increase in catalyst OCP. Interestingly, we found that the logarithm of the FAD rate showed a linear correlation with the OCP of the catalyst during the decay phase, which we quantitatively explained based on the reaction mechanism. This study presents a new discovery that bridges thermal and electrocatalysis.

Surface coverage control for dramatic enhancement of thermal CO oxidation by precise potential tuning of metal supported catalysts.

Chemical heterogeneous catalysis maximizes performance by controlling the interactions between the catalyst and the substrates. Steady-state catalytic rates depend on the heat of adsorption and the resultant coverage of adsorbates, which in turn reflects the electronic structure of the heterogeneous catalyst surfaces. This study aims to free the surface from high coverage of a kind of substance by externally controlling the electrochemical potential of the catalysts for improved thermal-catalytic rates. We employed aqueous CO oxidation at 295 K as a model reaction, where strong binding of chemisorbed CO (CO*) to the metal surfaces and its high coverage led to inhibition of O2 accessing the surface site. Based on the establishment of coverage-potential-performance correlation, our potential-controlling experiments used an electrochemical configuration to identify the appropriate potentials of Pt/C catalysts that can drastically enhance the CO2 formation rate through the thermal reaction pathway. An anodic potential was applied to suppress the high coverage of chemisorbed CO; consequently, the catalytic testing recorded a 5-fold increase in thermal CO2 formation compared to the open-circuit counterpart with a faradaic efficiency (FE) of over 400%. In situ infrared spectroscopy corroborates the potential-coverage correlation, where the suppression of high CO* coverage due to pinning the catalyst potential triggered the enhancement of thermal-catalytic contribution to CO2 formation. Our extended study employing other metal catalysts also exhibited FEs exceeding unity. This work establishes a universal methodology of electrochemical tools for thermal catalysis to precisely tune the electrochemical potential of solids and achieve green and innovative reactions.

Environmental high-voltage S/TEM combined with a quadrupole mass spectrometer for concurrent in situ structural characterization and detection of product gas molecules associated with chemical reactions.

We introduce herein a combined environmental high-voltage electron microscope and a quadrupole mass spectrometer to detect product gas species associated with chemical reactions occurring in the microscope, which allows new operando experiments of, for instance, observing catalytic reactions by concurrent high-resolution transmission electron microscope (TEM) observation. We demonstrate the preliminary results of redox reactions, where the product gas species are unambiguously detected, associated with the expected structural transformations observed with TEM.