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In situattenuated total reflection surface enhanced infrared absorption spectroscopy (ATR‐SEIRAS) is often used to investigate the near‐surface electrocatalytic reaction environment. However, there is a gap in directly correlating the near‐surface reaction environment with electrocatalytic reaction rates. To that end, we designed an electrochemical flow reactor foroperandoelectrochemical ATR‐SEIRAS and demonstrate its capability with the CO₂reduction reaction (CO₂RR). Roughened gold catalyst thin films are prepared on ATR silicon crystals as a model system to probe local species under CO₂RR conditions in 0.1 M KHCO₃. We measured changes in the interfacial CO₂concentration as a function of applied potential and electrolyte flow rate inoperando, allowing us to correlate the changes in reaction rates with the observed CO₂concentration. Including the choice of the catalyst and electrolyte, coupling hydrodynamic control with ATR‐SEIRAS in this platform enables investigations of how the local microenvironment affects the activity and selectivity of electrochemical reactions.

 

A cobalt porphyrin molecule, namely CoTcPP (TcPP = the dianion of meso -tetra(4-carboxyphenyl)porphyrin), is intercalated into zirconium phosphate (ZrP) layers as an effective way to heterogenize a porphyrin-based molecular electrocatalyst. Fourier-transform infrared (FT-IR) spectroscopy, X-ray powder diffraction (XRPD) measurements, UV-Vis spectroscopy, elemental mapping, energy dispersive X-ray (EDX) analysis, inductively coupled plasma mass spectrometry (ICP-MS) and X-ray photoelectron spectroscopy (XPS) were utilized to determine the successful intercalation of CoTcPP into ZrP. While the CoTcPP molecule is not amendable to be used as a heterogeneous catalyst in basic environment due to the carboxylic groups, the intercalated species (CoTcPP/ZrP) is effective towards water oxidation from KOH aqueous solution when utilized as a heterogeneous electrocatalyst and shows remarkable catalytic durability. Electrochemical results show that CoTcPP/ZrP requires an overpotential of 0.467 V to achieve a current density of 10 mA cm −2 while the pristine α-ZrP shows negligible electrocatalytic OER behavior. 

The electrochemical oxygen evolution reaction (OER) is the half-cell reaction for many clean-energy production technologies, including water electrolyzers and metal–air batteries. However, its sluggish kinetics hinders the performance of those technologies, impeding them from broader implementation. Recently, we reported the use of zirconium phosphate (ZrP) as a support for transition metal catalysts for the oxygen evolution reaction (OER). These catalysts achieve promising overpotentials with high mass activities. Herein, we synthesize ZrP structures with controlled morphology: hexagonal platelets, rods, cubes, and spheres, and subsequently modify them with Co( ii ) and Ni( ii ) cations to assess their electrochemcial OER behavior. Through inductively coupled plasma mass-spectrometry measurements, the maximum ion exchange capacity is found to vary based on the morphology of the ZrP structure and cation selection. Trends in geometric current density and mass activity as a function of cation selection are discussed. We find that the loading and coverage of cobalt and nickel species on the ZrP supports are key factors that control OER performance. 

The use of thin Ta₃N₅films in tandem Si‐Ta₃N₅photoelectrochemical (PEC) devices motivates understanding of the surface Ta₃N­₅properties, as they may have a strong effect on the device performance. The bulk and surface properties can change as a function of nitridation temperature; thus its effect is studied, ranging from 700 to 1000 °C, on the PEC performance, morphology, and composition of thin (10 nm) Ta₃N₅films deposited on planar and nanostructured Si substrates. Scanning electron microscopy (SEM), scanning Auger electron spectroscopy (AES), X‐ray photoelectron spectroscopy (XPS), and X‐ray diffraction (XRD) are employed to gain fundamental understanding in the differences of the Ta­₃N₅films. By controlling Ta₃N­₅morphology and composition with nitridation temperature, it is determined that Ta₃N₅with high crystallinity and surface N/Ta ratio, synthesized at 800 °C, yields the highest PEC performance with the earliest photocurrent onset and highest photocurrent. Samples nitrided at 700 °C have lower crystallinity and that likely leads to lower performance. For samples nitrided at temperatures above 800 °C, the N/Ta ratio decreases forming chemically reduced tantalum nitride phases, as well as N‐deficient and correspondingly O‐rich morphological domains that can adversely affect the PEC performance as hole‐blocking layers or O trap‐mediated recombination centers at the surface of Ta₃N₅.

 

In this work, a methodology is demonstrated to engineer gas diffusion electrodes for nonprecious metal catalysts. Highly active transition metal phosphides are prepared on carbon‐based gas diffusion electrodes with low catalyst loadings by modifying the O/C ratio at the surface of the electrode. These nonprecious metal catalysts yield extraordinary performance as measured by low overpotentials (51 mV at −10 mA cm⁻²), unprecedented mass activities (>800 A g⁻¹at 100 mV overpotential), high turnover frequencies (6.96 H₂s⁻¹at 100 mV overpotential), and high durability for a precious metal‐free catalyst in acidic media. It is found that a high O/C ratio induces a more hydrophilic surface directly impacting the morphology of the CoP catalyst. The improved hydrophilicity, stemming from introduced oxyl groups on the carbon electrode, creates an electrode surface that yields a well‐distributed growth of cobalt electrodeposits and thus a well‐dispersed catalyst layer with high surface area upon phosphidation. This report demonstrates the high‐performance achievable by CoP at low loadings which facilitates further cost reduction, an important part of enabling the large‐scale commercialization of non‐platinum group metal catalysts. The fabrication strategies described herein offer a pathway to lower catalyst loading while achieving high efficiency and promising stability on a 3D electrode.

 

The local microenvironment at the electrode‐electrolyte interface plays an important role in electrocatalytic performance. Herein, we investigate the effect of acid electrolyte anion identity on the oxygen reduction reaction (ORR) activity and selectivity of smooth Ag and Pd catalyst thin films. Cyclic voltammetry in perchloric, nitric, sulfuric, phosphoric, hydrochloric, and hydrobromic acid, at pH 1, reveals that Ag ORR activity trends as follows: HClO₄>HNO₃>H₂SO₄>H₃PO₄>HCl≫HBr, while Pd ORR activity trends as: HClO₄>H₂SO₄>HNO₃>H₃PO₄>HCl≫HBr. Moreover, rotating‐ring‐disk‐electrode selectivity measurements demonstrate enhanced 4e⁻selectivity on both Ag and Pd, by up to 35 %H₂O₂and 10 %H₂O₂respectively, in HNO₃compared to in HClO₄. Relating physics‐based modeling and experimental results, we postulate that ORR performance depends greatly on anion‐related phenomena in the double layer, for instance competitive adsorption and non‐covalent interactions.

 

Tandem photoelectrochemical water splitting cells utilizing crystalline Si and metal oxide photoabsorbers are promising for low‐cost solar hydrogen production. This study presents a device design and a scalable fabrication scheme for a tandem heterostructure photoanode: p⁺n black silicon (Si)/SnO₂interface/W‐doped bismuth vanadate (BiVO₄)/cobalt phosphate (CoPi) catalyst. The black‐Si not only provides a substantial photovoltage of 550 mV, but it also serves as a conductive scaffold to decrease charge transport pathlengths within the W‐doped BiVO₄shell. When coupled with cobalt phosphide (CoP) nanoparticles as hydrogen evolution catalysts, the device demonstrates spontaneous water splitting without employing any precious metals, achieving an average solar‐to‐hydrogen efficiency of 0.45% over the course of an hour at pH 7. This fabrication scheme offers the modularity to optimize individual cell components, e.g., Si nanowire dimensions and metal oxide film thickness, involving steps that are compatible with fabricating monolithic devices. This design is general in nature and can be readily adapted to novel, higher performance semiconducting materials beyond BiVO₄as they become available, which will accelerate the process of device realization.