Binary Pd−Ni Nanoalloy Particles over Carbon Support with Superior Alkaline Formate Fuel Electrooxidation Performance

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.

Nickel -supported PdM (M = Au and Ag) nanodendrites as formate oxidation (electro)catalytic anodes for direct fuel cells and hydrogen generation at room temperature

The study provides a proof of concept for the first time that unique palladium-gold (PdAu) and palladium-silver (PdAg) nanodendrites are bifunctional catalytic active sites for formate oxidation reactions (FORs) and formate dehydrogenation reactions (FDRs). The unique nanodendritic structure was developed via a simple galvanic displacement reaction for the direct growth of PdAu and PdAg nanodendrites on a nickel foam (PdAu/NiNF and PdAg/NiNF). These PdAu/NiNF and PdAg/NiNF electrodes exhibited 2.32 and 1.59 times higher specific activity than that of the commercial Pd/C electrode and promising stability toward FORs. Moreover, the PdAu/NiNF and PdAg/NiNF nanodendrites were also highly active and selective catalysts for hydrogen generation from a formate solution with turnover frequency (TOF) values of 311 h^-1 and 287 h^-1 respectively. Impressively, a passive air-breathing formate fuel cell with PdAu/NiNF used as an anode can yield an open-circuit voltage of 1.12 V and a peak power density of 21.7 mW cm^-2, which outperforms most others reported in the literature. PdAu and PdAg nanodendritic catalysts supported on a nickel foam demonstrate an open structure and uniform catalyst distribution and offer a promising nanoalloy for air-breathing formate fuel cells and on-site chemical hydrogen production systems.

Ultrathin PdCu Nanosheet as Bifunctional Electrocatalysts for Formate Oxidation Reaction and Oxygen Reduction Reaction

The development of robust nonplatinum electrocatalysts to enhance the performance of formate oxidation reaction (FOR) and oxygen reduction reaction (ORR) is one of the key issues for the commercialization of direct formate fuel cells (DFFCs), but still challenging. Herein, a structurally controlled 3D flower-like PdCu nanosheet (NS) catalyst is synthesized by a method of oil bath reduction under mild conditions as a bifunctional electrocatalyst for DFFCs. Under the dual tuning on the composition and intermetallic phase, the PdCu nanosheet catalyst exhibits 8.67 times higher mass activity for anodic formate oxidation reaction than the commercial Pd/C. For the cathodic ORR, a positive shift half-wave potential is obtained for PdCu nanosheets exceeding Pt/C. Moreover, after a long-term stability test, the current density of the PdCu nanosheet catalyst for FOR and ORR can be well maintained with the least activity decay. When the PdCu NSs are used as optimized anode and cathode electrodes for DFFCs enable a peak power density as high as 53 mW cm^-2 at room temperature, which is about 1.3 times higher than that of the commercial Pd/C and Pt/C as anode and cathode electrodes. This work provides a potential strategy to improve the catalytic performance of non-Pt-based nanocatalysts.

An Enhanced Oxidation of Formate on PtNi/Ni Foam Catalyst in an Alkaline Medium

In this study, a platinum-coated Ni foam catalyst (denoted PtNi/Ni foam) was investigated for the oxidation of the formate reaction (FOR) in an alkaline medium. The catalyst was fabricated via a two-step procedure, which involved an electroless deposition of the Ni layer using sodium hypophosphite as a reducing agent and the subsequent electrodeposition of the platinum layer. The PtNi/Ni foam catalyst demonstrated enhanced electrocatalytic activity for the FOR in an alkaline medium compared to the Ni/Ni foam catalyst and pure Pt electrode. Moreover, the PtNi/Ni foam catalyst promoted the FOR at more negative potentials than the Pt electrode. This contributed to a significant negative shift in the onset potential, indicating the high activity of the catalyst. Notably, in alkaline media with the PtNi/Ni foam catalyst, the FOR proceeds via a direct pathway mechanism without significant accumulation of poisonous carbonaceous species on the PtNi/Ni foam catalyst.

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.

An enhanced electrochemical CO2 reduction reaction on the SnOx–PdO surface of SnPd nanoparticles decorated on N-doped carbon fibers

Electrochemical reduction of CO₂ to formate on SnPd–NCF. The adsorbed bicarbonate ion promotes the protonation of CO₂˙⁻ to HCO₂⁻.