Voltage cycling process for the electroconversion of biomass-derived polyols

Interfacial Micro-Environment of Electrocatalysis and Its Applications for Organic Electro-Oxidation Reaction

Conventional designing principal of electrocatalyst is focused on the electronic structure tuning, on which effectively promotes the electrocatalysis. However, as a typical kind of electrode-electrolyte interface reaction, the electrocatalysis performance is also closely dependent on the electrocatalyst interfacial micro-environment (IME), including pH, reactant concentration, electric field, surface geometry structure, hydrophilicity/hydrophobicity, etc. Recently, organic electro-oxidation reaction (OEOR), which simultaneously reduces the anodic polarization potential and produces value-added chemicals, has emerged as a competitive alternative to oxygen evolution reaction, and the role IME played in OEOR is receiving great interest. Thus, this article provides a timely review on IME and its applications toward OEOR. In this review, the IME for conventional gas-involving reactions, as a contrast, is first presented, and then the recent progresses of IME toward diverse typical OEOR are summarized; especially, some representative works are thoroughly discussed. Additionally, cutting-edge analytical methods and characterization techniques are introduced to comprehensively understand the role IME played in OEOR. In the last section, perspectives and challenges of IME regulation for OEOR are shared.

Pulsed Electrolysis of Boron-Doped Carbon Dramatically Improves Impurity Tolerance and Longevity of H2O2 Production

Electrocatalytic water treatment has emerged in the limelight of scientific interest, yet its long-term viability remains largely in the dark. Herein, we present for the first time a comprehensive framework on how to optimize pulsed electrolysis to bolster catalyst impurity tolerance and overall longevity. By examining real wastewater constituents and assessing different catalyst designs, we deconvolute the complexities associated with key pulsing parameters to formulate optimal sequences that maximize operational lifetime. We showcase our approach for cathodic H2O2 electrosynthesis, selected for its widespread importance to wastewater treatment. Our results unveil superior performance for a boron-doped carbon catalyst over state-of-the-art oxidized carbon, with high selectivity (>75%) and near complete recoveries in overpotentials even in the presence of highly detrimental Ni2+ and Zn2+ impurities. We then adapt these fine-tuned settings, obtained under a three-electrode arrangement, for practical two-electrode operation using a novel strategy that conserves the desired electrochemical potentials at the catalytic interface. Even under various impurity concentrations, our pulses substantially improve long-term H2O2 production to 287 h and 35 times that attainable via conventional electrolysis. Our findings underscore the versatility of pulsed electrolysis necessary for developing more practical water treatment technologies.

Identification of Active Sites Formed on Cobalt Oxyhydroxide in Glucose Electrooxidation

Transition-metal-based oxyhydroxides are efficient catalysts in biomass electrooxidation towards fossil-fuel-free production of valuable chemicals. However, identification of active sites remains elusive. Herein, using cobalt oxyhydroxide (CoOOH) as the archetype and the electrocatalyzed glucose oxidation reaction (GOR) as the model reaction, we track dynamic transformation of the electronic and atomic structure of the catalyst using a suite of operando and ex situ techniques. We reveal that two types of reducible Co³⁺ -oxo species are afforded for the GOR, including adsorbed hydroxyl on Co³⁺ ion (μ₁ -OH-Co³⁺ ) and di-Co³⁺ -bridged lattice oxygen (μ₂ -O-Co³⁺ ). Moreover, theoretical calculations unveil that μ₁ -OH-Co³⁺ is responsible for oxygenation, while μ₂ -O-Co³⁺ mainly contributes to dehydrogenation, both as key oxidative steps in glucose-to-formate transformation. This work provides a framework for mechanistic understanding of the complex near-surface chemistry of metal oxyhydroxides in biomass electrorefining.

Microscopic Model for Cyclic Voltammetry of Porous Electrodes

Cyclic voltammetry (CV) is a widespread experimental technique for characterizing electrochemical devices such as supercapacitors. Despite its wide use, a quantitative relation between CV and microscopic properties of supercapacitors is still lacking. In this Letter, we use both the microscopic "stack-electrode" model and its equivalent circuit for predicting the cyclic voltammetry of electric double-layer formation in porous electrodes. We find that the dimensionless combination ωτ_{n}, with ω the scan frequency of the time-dependent potential and τ_{n} the relaxation timescale of the stack-electrode model, governs the CV curves and capacitance: the capacitance is scan-rate independent for ωτ_{n}≪1 and scan-rate dependent for ωτ_{n}≫1. With a single fit parameter and all other model parameters dictated by experiments, our model reproduces experimental CV curves over a wide range of ω. Meanwhile, the influence of the pore size distribution on the charging dynamics is investigated to explain the experimental data.

Anode Catalysts in CO2 Electrolysis: Challenges and Untapped Opportunities

The field of electrochemical carbon dioxide reduction has developed rapidly during recent years. At the same time, the role of the anodic half-reaction has received considerably less attention. In this Perspective, we scrutinize the reports on the best-performing CO2 electrolyzer cells from the past 5 years, to shed light on the role of the anodic oxygen evolution catalyst. We analyze how different cell architectures provide different local chemical environments at the anode surface, which in turn determines the pool of applicable anode catalysts. We uncover the factors that led to either a strikingly high current density operation or an exceptionally long lifetime. On the basis of our analysis, we provide a set of criteria that have to be fulfilled by an anode catalyst to achieve high performance. Finally, we provide an outlook on using alternative anode reactions (alcohol oxidation is discussed as an example), resulting in high-value products and higher energy efficiency for the overall process.

Alcohols electrooxidation coupled with H2 production at high current densities promoted by a cooperative catalyst

Electrochemical alcohols oxidation offers a promising approach to produce valuable chemicals and facilitate coupled H2 production. However, the corresponding current density is very low at moderate cell potential that substantially limits the overall productivity. Here we report the electrooxidation of benzyl alcohol coupled with H2 production at high current density (540 mA cm-2 at 1.5 V vs. RHE) over a cooperative catalyst of Au nanoparticles supported on cobalt oxyhydroxide nanosheets (Au/CoOOH). The absolute current can further reach 4.8 A at 2.0 V in a more realistic two-electrode membrane-free flow electrolyzer. Experimental combined with theoretical results indicate that the benzyl alcohol can be enriched at Au/CoOOH interface and oxidized by the electrophilic oxygen species (OH*) generated on CoOOH, leading to higher activity than pure Au. Based on the finding that the catalyst can be reversibly oxidized/reduced at anodic potential/open circuit, we design an intermittent potential (IP) strategy for long-term alcohol electrooxidation that achieves high current density (>250 mA cm-2) over 24 h with promoted productivity and decreased energy consumption.