Catalytically active highly metallic palladium on carbon support for oxidation of HCOO −

Electrochemical Redox Conversion of Formate to CO via Coupling Fe-Co Layered Double Hydroxides and Au Catalysts

Formate has been considered an inactive molecule and thus cannot be further reduced under CO2 reduction conditions, which limits its widespread application as feedstock. Here we present an electrochemical redox conversion of formate to CO through the potential-dependent generation of carbon dioxide radical anions (CO2 ⋅- ) on Fe-Co layered double hydroxides (Fe-Co LDHs) and the subsequent reduction of CO2 ⋅- to CO on Au catalysts. We present an electrodeposition protocol for the synthesis of Fe-Co LDHs with precise composition control and find that Fe1 Co4 exhibits a promising potential window for CO2 ⋅- formation between 1.14 and 1.4 V and an optimized potential at 1.24 V at a neutral pH condition. We further determined the formation of CO2 ⋅- at 1.24 V via electron paramagnetic resonance and CO2 at >1.4 V through differential electrochemical mass spectrometry. This work provides a redox chemistry route for converting formate into CO through a coupled slit parallel-plate electrode system.

Breaking scaling relationships in alkynol semi-hydrogenation by manipulating interstitial atoms in Pd with d-electron gain

Pd catalysts are widely used in alkynol semi-hydrogenation. However, due to the existence of scaling relationships of adsorption energies between the key adsorbed species, the increase in conversion is frequently accompanied by side reactions, thereby reducing the selectivity to alkenols. We report that the simultaneous increase in alkenol selectivity and alkynol conversion is achieved by manipulating interstitial atoms including B, P, C, S and N in Pd catalysts. A negative linear relationship is observed between the activation entropies of 2-methyl-3-butyn-2-ol and 2-methyl-3-buten-2-ol which is highly related to the filling of d-orbital of Pd catalysts by the modification of p-block elements. A catalyst co-modified by B and C atoms has the maximum d charge of Pd that achieves a 17-fold increase in the turn-over frequency values compared to the Lindlar catalysts in the semi-hydrogenation of 2-methyl-3-butyn-2-ol. When the conversion is close to 100%, the selectivity can be as high as 95%.

Circumventing the linear scaling relationship in the semi-hydrogenation is challenging. Here the authors report a method for breaking the scaling relationships using ordered mesoporous carbon-supported Pd nanocatalysts with d-electron gain by p-block atoms occupying interstitial sites in the lattice as a greener alternative to Lindlar catalysts for the selective hydrogenation of alkynols.

Benchmarking Catalysts for Formic Acid/Formate Electrooxidation

Energy production and consumption without the use of fossil fuels are amongst the biggest challenges currently facing humankind and the scientific community. Huge efforts have been invested in creating technologies that enable closed carbon or carbon neutral fuel cycles, limiting CO2 emissions into the atmosphere. Formic acid/formate (FA) has attracted intense interest as a liquid fuel over the last half century, giving rise to a plethora of studies on catalysts for its efficient electrocatalytic oxidation for usage in fuel cells. However, new catalysts and catalytic systems are often difficult to compare because of the variability in conditions and catalyst parameters examined. In this review, we discuss the extensive literature on FA electrooxidation using platinum, palladium and non-platinum group metal-based catalysts, the conditions typically employed in formate electrooxidation and the main electrochemical parameters for the comparison of anodic electrocatalysts to be applied in a FA fuel cell. We focused on the electrocatalytic performance in terms of onset potential and peak current density obtained during cyclic voltammetry measurements and on catalyst stability. Moreover, we handpicked a list of the most relevant examples that can be used for benchmarking and referencing future developments in the field.

Engineering Two-Dimensional PdAgRh Nanoalloys by Surface Reconstruction for Highly Active and Stable Formate Oxidation Electrocatalysis

Promoting the formate oxidation reaction (FOR) is central to develop promising direct formate fuel cells, but current electrocatalysts are suffering from low activity and ultrapoor stability. Herein, the ternary PdAgRh nanoalloys with ultrathin two-dimensional architecture are for the first time synthesized and employed as a novel class of electrocatalysts for the FOR. Benefitting from unique nanostructure as well as oxophilic Rh surface oxides, the Pd₅₅Ag₃₀Rh₁₅/C electrocatalyst demonstrates an exceptional FOR activity of 1.85 A mg_Pd^-1, showing a 4.74-fold improvement compared to the commercial Pd/C, and retains the current density of 150 mA mg_Pd^-1 after a long-term test, representing the greatest durability among all available FOR electrocatalysts. More strikingly, extending the upper limit potential (ULP) of cyclic voltammetry is revealed to facilitate the surface reconstruction of the Pd₅₅Ag₃₀Rh₁₅/C electrocatalyst to in situ form Ag surface oxides (Ag-O), resulting in a highly active and stable Pd/Ag-O interface at the atomic scale, which considerably boost the FOR performance. In particular, the reconstructed Pd₅₅Ag₃₀Rh₁₅/C electrocatalyst exhibits a mass activity of 3.26 A mg_Pd^-1 with 74.2% of initial activity retained after 1000 cycles. This work showcases an effective strategy to tune surface reconstruction on multimetallic nanoalloys for robust FOR electrocatalysts and beyond.

Unexpectedly high stability and surface reconstruction of PdAuAg nanoparticles for formate oxidation electrocatalysis

High-performance Pd-based nanocatalysts for alkaline methanol and formate fuel cells have stimulated widespread attention. Hence, a series of ternary Pd-Au-Ag nanoalloys have been synthesized on carbon nanotubes, which demonstrate promising activity and unexpectedly high stability for the formate oxidation reaction (FOR) in alkaline medium. The ternary Pd3Au3Ag1 nanoalloy catalyst showed an initial mass activity of 4.51 A mgPd-1 and a retained mass activity of 1.32 A mgPd-1 after chronoamperometric measurement for 3600 s, which are superior to the best values for all FOR catalysts reported so far. The Pd3Au3Ag1 catalyst also showed a good specific activity of 4.32 mA cm-2 for the methanol oxidation reaction. Furthermore, surface reconstruction of the Pd3Au3Ag1 nanoalloy was observed during FOR, where the activity of Pd3Au3Ag1 catalysts increased up to 33% and the cycling durability retained 55% after cyclic voltammetry with the upper potential of 1.7 V. The FOR enhancement is attributed to the formation of mixed oxidation-state Ag sites and the increase in the Pd surface coverage, and provides a new prospect for the design of ternary nanoalloy electrocatalysts for various fuel oxidation reactions.

Catalytic activity of palladium-doped silver dilute nanoalloys for formate oxidation from a theoretical perspective

The large-scale practical application of formate oxidation reaction (FOR) catalysts is hindered by their low activity and high cost. Herein, for the first time, a series of Pd-doped Ag dilute nanoalloys is demonstrated to have high catalytic activity in FOR with reduced consumption of Pd metals through density functional theory calculations, where the effects of potential, solvent and spin on catalytic performance are discussed. The Pd1Ag(111) single-atom alloy (SAA) exhibits higher FOR catalytic activity as reflected by the low limiting potential of 0.026 eV for the direct association path and a value of 0.084 eV for the direct dissociation path, and the lowest activation energy of 0.774 eV for the rate-determining-step in the direct dissociation path compared with Pd2Ag(111) and Pd3Ag(111) dilute alloys. Pd1Ag(111) SAA exhibits an extremely narrow sharp peak in the partial density of states from -0.75 to -2.0 eV, which is due to the free-atom-like electronic structure of the single Pd atom. The isolated Pd single atom is more stable by -0.041 and -0.097 eV, respectively, than the aggregated Pd2 and Pd3 atom clusters on the Ag(111) surface, which verifies the potential application of Pd1Ag(111) SAA in experiments. Overall, this work further elucidates the theoretical profile of FOR and provides a new strategy for designing the catalytic reaction at the atomic level.

In situ high-potential-driven surface restructuring of ternary AgPd-Ptdilute aerogels with record-high performance improvement for formate oxidation electrocatalysis

Engineering nanoparticle surfaces driven by various gas atmospheres has attracted intensive attention in the design of efficient electrocatalysts for sustainable energy applications. However, the development of a more facile and efficient in situ engineering strategy under electrochemical testing conditions to achieve surface-reconstruction-induced high performance is significantly lacking. Herein, for the first time, we report in situ high-potential-driven restructuring in ternary AgPdPt aerogels with dilute Pt (AgPd-Ptdilute) during the electrochemical cyclic voltammetry testing for the alkaline formate oxidation reaction (FOR), in which the upper potential limit is ingeniously extended to the Ag redox region. Impressively, the resulting AgPd-Ptdilute aerogel displayed remarkable structural and compositional reconstruction in an alkaline environment. Our comprehensive results revealed that the high-potential cycling induces unique Ag outward diffusion to form an enriched PdPt metallic surface atomically coupled with amorphous Ag2O, which provides more opportunities to expose abundant active sites and induce robust electronic structure modulation. Notably, the surface-restructured AgPd-Ptdilute aerogel achieved record-high activity for FOR when the upper potential limit was extended to 1.3 V, exhibiting an unprecedented 5-fold improvement in activity compared to that of the commercial Pd/C. Moreover, it also offered greatly enhanced electrochemical stability with negligible activity decay after 500 cycles. This work gives a good understanding of surface reconstruction during such a novel high-potential-driven cycling process and opens a new door to designing more efficient electrocatalysts for FOR and beyond.