142 research outputs found
Effects of Surface Roughness on the Electrochemical Reduction of COā over Cu
We have investigated the role of surface roughening on the COā reduction reaction (COāRR) over Cu. The activity and product selectivity of Cu surfaces roughened by plasma pretreatment in Ar, Oā, or Nā were compared with that of electrochemically polished Cu samples. Differences in total and product current densities, the ratio of current densities for HER (the hydrogen evolution reaction) to COāRR, and the ratio of current densities for Cāā to Cā products depend on the electrochemically active surface and are nearly independent of plasma composition. Theoretical analysis of an electropolished and roughened Cu surface reveals a higher fraction of undercoordinated Cu sites on the roughened surface, sites that bind CO preferentially. Roughened surfaces also contain square sites similar to those on a Cu(100) surface but with neighboring step sites, which adsorb OCāCOH, a precursor to Cāā products. These findings explain the increases in the formation of oxygenates and hydrocarbons relative to CO and the ratio of oxygenates to hydrocarbons observed with increasing surface roughness
Balancing Surface Passivation and Catalysis with Integrated BiVO_4/(Fe-Ce)O_x Photoanodes in pH 9 Borate Electrolyte
The performance of oxygen-evolving photoanodes based on bismuth vanadate (BiVO_4) is critically determined by the surface coating. While these coatings passivate surface defects, transport photogenerated holes, protect against corrosion, and aid catalysis, their optimal composition changes with operating pH, thus affecting overall performance. We use high-throughput photoelectrochemistry methods to map photoanode performance to enable the discovery of optimal composition and loading of Ce-rich sputter-deposited (FeāCe)O_x overlayers on undoped BiVO_4 in pH 9 borate buffer electrolyte. The optimal composition is found to be 20% Fe and 80% Ce with an optimal Fe + Ce metal loading of 0.9 nmol mm^(ā2). Analysis of the composition and loading dependence of (i) the photocurrent transients upon illumination toggling, (ii) stabilized photocurrent densities, and (iii) photogenerated hole-transfer efficiency reveals the confluence of phenomena that gives rise to the optimal performance yielding nearly perfect transfer efficiency over a narrow composition window
Effects of Surface Roughness on the Electrochemical Reduction of COā over Cu
We have investigated the role of surface roughening on the COā reduction reaction (COāRR) over Cu. The activity and product selectivity of Cu surfaces roughened by plasma pretreatment in Ar, Oā, or Nā were compared with that of electrochemically polished Cu samples. Differences in total and product current densities, the ratio of current densities for HER (the hydrogen evolution reaction) to COāRR, and the ratio of current densities for Cāā to Cā products depend on the electrochemically active surface and are nearly independent of plasma composition. Theoretical analysis of an electropolished and roughened Cu surface reveals a higher fraction of undercoordinated Cu sites on the roughened surface, sites that bind CO preferentially. Roughened surfaces also contain square sites similar to those on a Cu(100) surface but with neighboring step sites, which adsorb OCāCOH, a precursor to Cāā products. These findings explain the increases in the formation of oxygenates and hydrocarbons relative to CO and the ratio of oxygenates to hydrocarbons observed with increasing surface roughness
Correlating Oxidation State and Surface Area to Activity from Operando Studies of Copper CO Electroreduction Catalysts in a Gas-fed Device
The rational design of high-performance electrocatalysts requires a detailed understanding of dynamic changes in catalyst properties, including oxidation states, surface area, and morphology under realistic working conditions. Oxide-derived Cu catalysts exhibit a remarkable selectivity toward multicarbon products for the electrochemical CO reduction reaction (CORR), but the exact role of the oxide remains elusive for explaining the performance enhancements. Here, we used operando X-ray absorption spectroscopy (XAS) coupled with simultaneous measurements of the catalyst activity and selectivity by gas chromatography (GC) to study the relationship between oxidation states of Cu-based catalysts and the activity for ethylene (CāHā) production in a CO gas-fed cell. By utilizing a custom-built XAS cell, oxidation states of Cu catalysts can be probed in device-relevant settings and under high current densities (>80 mA cmā»Ā²) for the CORR. By employing an electrochemical oxidation process, we found that the Cu oxidation states and specific ion species do not correlate with CāHā production. The difference in the CORR activity is also investigated in relation to electrochemical surface area (ECSA) changes. While the hydrogen evolution reaction (HER) activity is positively correlated to the ECSA changes, the increased CāHā activity is not proportional to the ECSA. Ex situ characterization from microscopic techniques suggests that the changes in the CāHā activity and selectivity may arise from a morphological transformation that evolves into a more active structure. These comprehensive results give rise to the development of a cell regeneration method that can restore the performance of the Cu catalyst without cell disassembly. Our study establishes a basis for the rational design of highly active electrocatalysts for broad-range reactions in a gas-fed device
A nanoporous capacitive electrochemical ratchet for continuous ion separations
Directed ion transport in liquid electrolyte solutions underlies numerous
phenomena in nature and industry including neuronal signaling, photosynthesis
and respiration, electrodialysis for desalination, and recovery of critical
materials. Here, we report the first demonstration of an ion pump that drives
ions in aqueous electrolytes against a force using a capacitive ratchet
mechanism. Our ratchet-based ion pumps utilize the non-linear capacitive nature
of electric double layers for symmetry breaking which drives a net
time-averaged ion flux in response to a time varying input signal. Since the
devices are driven by a non-linear charging and discharging of double layers,
they do not require redox reactions for continual operation. Ratchet-based ion
pumps were fabricated by depositing thin gold layers on the two surfaces of
anodized alumina wafers, forming nanoporous capacitor-like structures. Pumping
occurs when a wafer is placed between two compartments of aqueous electrolyte
and the electric potential across it is modulated. In response to various input
signals, persistent ionic voltages and sustained currents were observed,
consistent with net unidirectional ion transport, even though conduction
through the membrane was non-rectifying. The generated ionic power was used in
conjunction with an additional shunt pathway to demonstrate electrolyte
demixing
Decacyclene Trianhydride at Functional Interfaces: An Ideal Electron Acceptor Material for Organic Electronics
We report the interface energetics of decacyclene trianhydride (DTA) monolayers on top of two distinct model surfaces, namely, Au(111) and Ag(111). On the latter, combined valence band photoemission and X-ray absorption measurements that access the occupied and unoccupied molecular orbitals, respectively, reveal that electron transfer from substrate to surface sets in. Density functional theory calculations confirm our experimental findings and provide an understanding not only of the photoemission and X-ray absorption spectral features of this promising organic semiconductor but also of the fingerprints associated with the interface charge transfer
Recommended from our members
Discovery of FeāCe Oxide/BiVO_4 Photoanodes through Combinatorial Exploration of NiāFeāCoāCe Oxide Coatings
An efficient photoanode is a prerequisite for a viable solar fuels technology. The challenges to realizing an efficient photoanode include the integration of a semiconductor light absorber and a metal oxide electrocatalyst to optimize corrosion protection, light trapping, hole transport, and photocarrier recombination sites. To efficiently explore metal oxide coatings, we employ a high-throughput methodology wherein a uniform BiVO_4 film is coated with 858 unique metal oxide coatings covering a range of metal oxide loadings and the full (NiāFeāCoāCe)O_x pseudoquaternary composition space. Photoelectrochemical characterization of the photoanodes reveals that specific combinations of metal oxide composition and loading provide up to a 13-fold increase in the maximum photoelectrochemical power generation for oxygen evolution in pH 13 electrolyte. Through mining of the high-throughput data we identify composition regions that form improved interfaces with BiVO_4. Of particular note, integrated photoanodes with catalyst compositions in the range Fe_((0.4ā0.6))Ce_((0.6ā0.4))O_x exhibit high interface quality and excellent photoelectrochemical power conversion. Scaled-up inkjet-printed electrodes and photoanodic electrodeposition of this composition on BiVO_4 confirms the discovery and the synthesis-independent interface improvement of (FeāCe)O_x coatings on BiVO_4
Balancing Surface Passivation and Catalysis with Integrated BiVO_4/(Fe-Ce)O_x Photoanodes in pH 9 Borate Electrolyte
The performance of oxygen-evolving photoanodes based on bismuth vanadate (BiVO_4) is critically determined by the surface coating. While these coatings passivate surface defects, transport photogenerated holes, protect against corrosion, and aid catalysis, their optimal composition changes with operating pH, thus affecting overall performance. We use high-throughput photoelectrochemistry methods to map photoanode performance to enable the discovery of optimal composition and loading of Ce-rich sputter-deposited (FeāCe)O_x overlayers on undoped BiVO_4 in pH 9 borate buffer electrolyte. The optimal composition is found to be 20% Fe and 80% Ce with an optimal Fe + Ce metal loading of 0.9 nmol mm^(ā2). Analysis of the composition and loading dependence of (i) the photocurrent transients upon illumination toggling, (ii) stabilized photocurrent densities, and (iii) photogenerated hole-transfer efficiency reveals the confluence of phenomena that gives rise to the optimal performance yielding nearly perfect transfer efficiency over a narrow composition window
- ā¦