Extrinsic hydrophobicity-controlled silver nanoparticles as efficient and stable catalysts for CO2 electrolysis.

To realize economically feasible electrochemical CO2 conversion, achieving a high partial current density for value-added products is particularly vital. However, acceleration of the hydrogen evolution reaction due to cathode flooding in a high-current-density region makes this challenging. Herein, we find that partially ligand-derived Ag nanoparticles (Ag-NPs) could prevent electrolyte flooding while maintaining catalytic activity for CO2 electroreduction. This results in a high Faradaic efficiency for CO (>90%) and high partial current density (298.39 mA cm‒2), even under harsh stability test conditions (3.4 V). The suppressed splitting/detachment of Ag particles, due to the lipid ligand, enhance the uniform hydrophobicity retention of the Ag-NP electrode at high cathodic overpotentials and prevent flooding and current fluctuations. The mass transfer of gaseous CO2 is maintained in the catalytic region of several hundred nanometers, with the smooth formation of a triple phase boundary, which facilitate the occurrence of CO2RR instead of HER. We analyze catalyst degradation and cathode flooding during CO2 electrolysis through identical-location transmission electron microscopy and operando synchrotron-based X-ray computed tomography. This study develops an efficient strategy for designing active and durable electrocatalysts for CO2 electrolysis.

Ultrasound-guided genitofemoral nerve block for femoral arterial access gain and closure: a randomized controlled trial.

OBJECTIVES: This study aimed to compare the analgesic efficacy and safety of the femoral branch block of the genitofemoral nerve (FBB) versus local infiltration anesthesia (LIA) for femoral arterial access gain and closure. METHODS: Eighty-two patients (age, 64.8 ± 10.9 years; female, 30.5%) undergoing endovascular procedures using 5-Fr femoral sheath were assigned to either FBB (n = 41) or LIA (n = 41). In both groups, 2% lidocaine HCL with 1:100,000 epinephrine was used as an anesthetic solution. Pain scores during access gain and closure were evaluated using a visual analog scale (score 0-10), patient satisfaction levels with the quality of anesthesia were scored on a 7-point Likert scale, and adverse events were recorded. RESULTS: The primary endpoint, pain scores during access closure, was significantly lower in the FBB group than in the LIA group (0.1 ± 0.37 vs 1.73 ± 0.92; p < 0.001). The FBB group also had significantly lower pain scores during access gain compared to the LIA group (0.83 ± 0.83 vs 2.78 ± 1.26; p < 0.001). There was an inverse relationship between pain scores and FBB after adjustment for age, gender, and body mass index (p < 0.001). FBB group reported significantly higher satisfaction with anesthesia quality compared to the LIA group (6.49 ± 0.64 vs 4.05 ± 1.05; p < 0.001). No complications were recognized in either group. CONCLUSIONS: Ultrasound-guided genitofemoral nerve blocks offered better acute pain relief and higher patient satisfaction than LIA during femoral arterial access gain and closure. CLINICAL RELEVANCE STATEMENT: In this prospective randomized controlled trial, ultrasound-guided genitofemoral nerve blocks offered better acute pain relief than local infiltration anesthesia, resulting in enhanced patient satisfaction. KEY POINTS: • FBB provided better pain relief during access gain and closure than LIA. • FBB offered higher patient satisfaction with the quality of anesthesia than LIA. • No anesthesia-related or access site complications were recognized in either treatment group.

Evaluation of the Antiviral Efficacy of Subcutaneous Nafamostat Formulated with Glycyrrhizic Acid against SARS-CoV-2 in a Murine Model.

The ongoing COVID-19 pandemic highlights the urgent need for effective antiviral agents and vaccines. Drug repositioning, which involves modifying existing drugs, offers a promising approach for expediting the development of novel therapeutics. In this study, we developed a new drug, MDB-MDB-601a-NM, by modifying the existing drug nafamostat (NM) with the incorporation of glycyrrhizic acid (GA). We assessed the pharmacokinetic profiles of MDB-601a-NM and nafamostat in Sprague-Dawley rats, revealing rapid clearance of nafamostat and sustained drug concentration of MDB-601a-NM after subcutaneous administration. Single-dose toxicity studies showed potential toxicity and persistent swelling at the injection site with high-dose administration of MDB-601a-NM. Furthermore, we evaluated the efficacy of MDB-601a-NM in protecting against SARS-CoV-2 infection using the K18 hACE-2 transgenic mouse model. Mice treated with 60 mg/kg and 100 mg/kg of MDB-601a-NM exhibited improved protectivity in terms of weight loss and survival rates compared to the nafamostat-treated group. Histopathological analysis revealed dose-dependent improvements in histopathological changes and enhanced inhibitory efficacy in MDB-601a-NM-treated groups. Notably, no viral replication was detected in the brain tissue when mice were treated with 60 mg/kg and 100 mg/kg of MDB-601a-NM. Our developed MDB-601a-NM, a modified Nafamostat with glycyrrhizic acid, shows improved protectivity against SARS-CoV-2 infection. Its sustained drug concentration after subcutaneous administration and dose-dependent improvements makes it a promising therapeutic option.

Gadoxetate disodium-enhanced MRI for diagnosis of hepatocellular carcinoma in patients with chronic liver disease: late portal venous phase may improve identification of enhancing capsule.

PURPOSE: To investigate added value of late portal venous phase (LPVP) for identification of enhancing capsule (EC) on gadoxetate disodium-enhanced MRI (GD-MRI) for diagnosing hepatocellular carcinoma (HCC) in patients with chronic liver disease (CLD). METHODS: This retrospective study comprised 116 high-risk patients with 128 pathologically proven HCCs who underwent GD-MRI including arterial phase, conventional portal venous phase (CPVP, 60 s), LPVP (mean, 104.4 ± 6.7 s; range, 90-119 s), and transitional phase (TP, 3 min). Two independent radiologists assessed the presence of major HCC features, including EC on CPVP and/or TP (CPVP/TP) and EC on LPVP. The frequency of EC was compared on GD-MRI between with and without inclusion of LPVP. The radiologists assigned Liver Imaging Reporting and Data System (LI-RADS) v2018 categories before and after identifying EC on LPVP. RESULTS: Of the total 128 HCCs, 74 and 73 revealed EC on CPVP/TP for reviewer 1 and 2, respectively. After inclusion of LPVP, each reviewer identified seven more EC [Reviewer 1, 57.8% (74/128) vs. 63.3% (81/128); Reviewer 2, 57.0% (73/128) vs. 62.5% (80/128); P = 0.016, respectively]. Sensitivities of LR-5 assignment for diagnosing HCCs were not significantly different in GD-MRI with or without LPVP for EC identification [Reviewer 1, 71.9% (92/128) vs. 72.7% (93/128); Reviewer 2, 75.0% (96/128) vs. 75.8% (97/128); P = 1.000, respectively]. CONCLUSION: Including the LPVP in GD-MRI may improve identification of EC of HCC in patients with CLD. However, LI-RADS v2018 using GD-MRI showed comparable sensitivity for diagnosing HCC regardless of applying LPVP for EC.

Imaging-Guided Deployment of a Balloon-Based Vascular Closure Device in Routine Clinical Practice.

This study evaluated the feasibility and safety of imaging-guided deployment of a Mynx Control device (Cordis, Miami Lakes, Florida) at the femoral access. A total of 201 Mynx devices were used under imaging guidance in 137 patients (mean age, 64.18 years ± 13.8; male, 68.6%) between June 2020 and February 2022. A 5-F sheath was used in 176 (87.6%) procedures, a 6-F sheath was used in 17 (8.5%) procedures, and a 7-F sheath was used in 8 (4%) procedures. Indicator errors occurred in 9 (4.5%) procedures. However, technical success was achieved via manipulation under imaging guidance in all procedures. The mean time to hemostasis was 3.3 minutes ± 0.5, and the clinical success rate was 100%. The mean length of hospital stay was 7 days ± 7.5. After 4 (2%) procedures, small hematomas reabsorbed spontaneously. Imaging-guided deployment of a Mynx Control device is a feasible and safe option for access site closure. Even after an indicator error, successful hemostasis was achieved via real-time interaction.

Prevalence and clinical significance of anatomic variant in cephalic arch on preoperative mapping venography.

The aim of the current study was to determine the prevalence of anatomic variant in cephalic arch on preoperative mapping venography and evaluate patency rates and predictors of patency in patients with brachiocephalic fistulas. The prevalence of anatomic variant in cephalic arch was retrospectively evaluated in 1004 consecutive patients who underwent bilateral preoperative mapping venography from July 2006 to December 2018 in a single center. The overall prevalence of anatomic variant in cephalic arch was 17.2% (173/1004). For patency analysis, 128 patients with brachiocephalic fistulas were divided into two groups: a standard anatomy (SA) group (n = 97) and a variant anatomy (VA) group (n = 31). There were no significant differences in clinical characteristics between the two groups. The primary patency rate did not differ significantly between the two groups. The secondary patency rate was significantly (p = 0.009) lower in the VA group than in the SA group. Older age (HR 1.03; 95% CI 1.01-1.05; p = 0.007) was a negative predictor of primary patency, and antiplatelet agent (HR 0.53; 95% CI 0.33-0.84; p = 0.007) and large-diameter cephalic vein (HR 0.52; 95% CI 0.31-0.86; p = 0.012) were positive predictors of primary patency. Older age (HR 1.04; 95% CI 1.01-1.07; p = 0.011) and anatomic variant in cephalic arch (HR 2.9; 95% CI 1.19-7.06; p = 0.019) were negative predictors of secondary patency. The current study provides insight into the clinical significance of anatomic variant in cephalic arch. Anatomic variant in cephalic arch should be considered as a potential risk factor for decreased patency of brachiocephalic fistula during preoperative planning.

Modified Surgical Drain-Guided Percutaneous Catheter Drainage of Postoperative Fluid Collection in Inaccessible Locations.

PURPOSE: To investigate the feasibility and safety of a modified surgical drain-guided percutaneous catheter drainage technique for postoperative fluid collection in inaccessible locations. MATERIALS AND METHODS: The modified technique was used in 24 patients (age, 58.6 years ± 11.3; men, 58.3%) from September 2015 to March 2021. All fluid collections had no safe access route on preprocedural computed tomography (CT) images. Every patient had a long (>20 cm) and tortuous surgical drain, which prevented the use of conventional surgical drain exchange. A favorable midpoint of the surgical drain tract was punctured under either ultrasound or fluoroscopic guidance, and a guide wire was advanced into the fluid collection. Technical success was defined as the successful placement of a drainage catheter, and clinical success was defined as the complete evacuation of fluid collection without recurrence. Follow-up was performed using CT images and a chart review. Adverse events within 30 days of the procedure were evaluated. RESULTS: Target fluid collections in the pelvic cavity (n = 9); subphrenic (n = 7), peripancreatic (n = 4), and subhepatic spaces (n = 3); and abdominal cavity (n = 1) were drained using catheters measuring 7-10.2 F in diameter and 25-30 cm in length. The technical success rate was 91.7% (22/24), and the clinical success rate was 90.9% (20/22). No procedure-related or catheter-related adverse events were observed. The median follow-up period was 8.2 months (range, 10-1,721 days). CONCLUSIONS: The modified surgical drain-guided percutaneous catheter drainage technique is a useful alternative when conventional exchange techniques cannot be used because of long and tortuous surgical drain paths.

Exploring dopant effects in stannic oxide nanoparticles for CO2 electro-reduction to formate.

The electrosynthesis of formate from CO2 can mitigate environmental issues while providing an economically valuable product. Although stannic oxide is a good catalytic material for formate production, a metallic phase is formed under high reduction overpotentials, reducing its activity. Here, using a fluorine-doped tin oxide catalyst, a high Faradaic efficiency for formate (95% at 100 mA cm-2) and a maximum partial current density of 330 mA cm-2 (at 400 mA cm-2) is achieved for the electroreduction of CO2. Furthermore, the formate selectivity (≈90%) is nearly constant over 7 days of operation at a current density of 100 mA cm-2. In-situ/operando spectroscopies reveal that the fluorine dopant plays a critical role in maintaining the high oxidation state of Sn, leading to enhanced durability at high current densities. First-principle calculation also suggests that the fluorine-doped tin oxide surface could provide a thermodynamically stable environment to form HCOO* intermediate than tin oxide surface. These findings suggest a simple and efficient approach for designing active and durable electrocatalysts for the electrosynthesis of formate from CO2.

Electrode reconstruction strategy for oxygen evolution reaction: maintaining Fe-CoOOH phase with intermediate-spin state during electrolysis.

Computational calculations and experimental studies reveal that the CoOOH phase and the intermediate-spin (IS) state are the key factors for realizing efficient Co-based electrocatalysts for the oxygen evolution reaction (OER). However, according to thermodynamics, general cobalt oxide converts to the CoO2 phase under OER condition, retarding the OER kinetics. Herein, we demonstrate a simple and scalable strategy to fabricate electrodes with maintaining Fe-CoOOH phase and an IS state under the OER. The changes of phase and spin states were uncovered by combining in-situ/operando X-ray based absorption spectroscopy and Raman spectroscopy. Electrochemical reconstruction of chalcogenide treated Co foam affords a highly enlarged active surface that conferred excellent catalytic activity and stability in a large-scale water electrolyzer. Our findings are meaningful in that the calculated results were experimentally verified through the operando analyses. It also proposes a new strategy for electrode fabrication and confirms the importance of real active phases and spin states under a particular reaction condition.

Diaphragmatic perforation after transcatheter arterial chemoembolization of hepatocellular carcinoma via inferior phrenic artery: a case report.

BACKGROUND: Transcatheter arterial chemoembolization (TACE) via the inferior phrenic artery has been recognized to have its own therapeutic role without causing serious procedural complications. We report a case of diaphragmatic perforation after repeated TACE sessions conducted via the right inferior phrenic artery. CASE PRESENTATION: A 43-year-old man diagnosed with hepatocellular carcinoma was admitted to the hospital with a chief complaint of cough. The patient underwent TACE via the right inferior phrenic artery 3 months prior and was discharged without specific complications. Physical examination revealed decreased breathing sounds in the right lower lung zone. Chest radiograph demonstrated a small right pleural effusion. Chest CT scan revealed a small diaphragmatic perforation. The patient was unable to undergo surgical exploration, and a follow-up CT scan after 2 months revealed progression of the right diaphragmatic perforation with massive herniation of omental fat into the thoracic cavity. CONCLUSIONS: Although TACE via the inferior phrenic artery is a relatively safe procedure, it can be associated with rare but serious complications after repeated procedures. This is a rare case report of diaphragmatic perforation after TACE via the right inferior phrenic artery. Early recognition and prompt surgical management are essential to prevent catastrophic outcomes.

Arterioureteral fistula: overview of clinical characteristics, endovascular management, and outcomes.

BACKGROUND: Arterioureteral fistula (AUF) is a condition resulting from the pathologic connection between the ureter and the artery. Despite the low incidence, it can lead to devastating clinical consequences due to massive hematuria with a considerable mortality rate. MATERIAL AND METHODS: From January 2009 to December 2018, eight patients with AUF from two tertiary referral centers were included. Clinical data including presenting symptoms, previous pelvic surgery or radiotherapy, indwelling ureteral stents, primary vascular pathology, angiographic findings, type of treatment, survival, and recurrence were analyzed. RESULTS: All eight patients (six women, mean age 62.4 ± 14.5 years) presented with macroscopic hematuria and were successfully treated by endovascular management. One patient developed AUF due to an underlying iliac artery aneurysm, and the rest were due to secondary causes. Six patients had a history of an indwelling ureteral stent for a median of 5.5 months (1-84 months). All of the patients were successfully treated by endovascular management. For the median follow up of 987 days, three patients had recurrence of hematuria in a mean of 6.3 months, two patients were treated by surgery, while one was treated by endovascular treatment. CONCLUSION: AUF should be confirmed through a purposeful iliac angiogram or ureterography when suspected based on a relevant history or CT findings. AUF can be successfully treated by endovascular management. The surgical option should be considered in cases of recurrence. ABBREVIATIONS: AUF: arterioureteral fistula; CIA: common iliac artery; DJ: double J; EIA: external iliac artery; IIA: internal iliac artery; NBCA: N-butyl cyanoacrylate; PCN: percutaneous nephrostomy.

Enhanced production of ginsenoside Rh2(S) from PPD-type major ginsenosides using BglSk cloned from Saccharibacillus kuerlensis together with two glycosidase in series.

BACKGROUND: Ginsenoside Rh2(S) is a promising compound for the prevention of various kinds of cancers, inflammation, and diabetes. However, due to its low concentration (<0.02%), researchers are still trying to find an efficient glycoside hydrolase for the scaled-up production of Rh2(S). METHOD: Three glycoside hydrolases (BglBX10, Abf22-3, and BglSk) were cloned in Escherichia coli BL21 (DE3) and the expressed recombinant enzyme was used for the scaled-up production of Rh2(S) through the conversion of PPD-type (protopanaxadiol) major ginsenosides (Rb1, Rc, and Rd, except Rb2) extracted from Korean red ginseng. Specific and specialized bioconversion pathways were designed that evolved the initial bioconversion of PPD-mix â†’ Rg3(S) â†’ Rh2(S). The reaction was started with 50 mg/mL of PPD-mix, 20 mg/mL of BglBX10, Abf22-3, and BglSk in series, respectively. The process was completed in a 10 L jar fermenter with a 5 L working volume at 37 °C for 48 hrs. RESULTS: The designed bioconversion pathways show that Abf22-3 and BglBX10 were responsible for the conversion of Rb1, Rc and Rd â†’ Rg3(S), and then Rg3(S) was completely transformed to Rh2(S) by BglSk. As a result, 15.1 g of ginsenoside Rh2(S) with 98.0 ± 0.2% purity was obtained after strict purification using the Prep-HPLC system with a 100 φ diameter column. Additionally, BglSk was also investigated for its production activity with seven different kinds of PPD-mix type ginsenosides. CONCLUSION: Our pilot data demonstrate that BglSk is a suitable enzyme for the gram unit production of ginsenoside Rh2(S) at the industrial level.

High crystallinity design of Ir-based catalysts drives catalytic reversibility for water electrolysis and fuel cells.

The voltage reversal of water electrolyzers and fuel cells induces a large positive potential on the hydrogen electrodes, followed by severe system degradation. Applying a reversible multifunctional electrocatalyst to the hydrogen electrode is a practical solution. Ir exhibits excellent catalytic activity for hydrogen evolution reactions (HER), and hydrogen oxidation reactions (HOR), yet irreversibly converts to amorphous IrOx at potentials > 0.8 V/RHE, which is an excellent catalyst for oxygen evolution reactions (OER), yet a poor HER and HOR catalyst. Harnessing the multifunctional catalytic characteristics of Ir, here we design a unique Ir-based electrocatalyst with high crystallinity for OER, HER, and HOR. Under OER operation, the crystalline nanoparticle generates an atomically-thin IrOx layer, which reversibly transforms into a metallic Ir at more cathodic potentials, restoring high activity for HER and HOR. Our analysis reveals that a metallic Ir subsurface under thin IrOx layer can act as a catalytic substrate for the reduction of Ir ions, creating reversibility. Our work not only uncovers fundamental, uniquely reversible catalytic properties of nanoparticle catalysts, but also offers insights into nanocatalyst design.

Sharp Needle Recanalization Technique for Peripheral Hemodialysis Arteriovenous Fistula Occlusion.

PURPOSE: To determine the efficacy of a percutaneous sharp needle recanalization technique for the treatment of peripheral hemodialysis arteriovenous fistula (AVF) occlusion. MATERIALS AND METHODS: This study included 13 patients (14 procedures) between May 2010 and February 2020 with non-thrombotic AVF occlusion wherein guidewire passage through the occluded segment had failed. We successfully passed the guidewire through the occluded segment using a sharp needle recanalization technique with Chiba or Colapinto needles, under ultrasound or fluoroscopic guidance. The type of AVF, site and length of occlusion, technical success, complications, and long-term patency were analyzed. RESULTS: Technical success was achieved in 12 (85.7%) out of 14 procedures. The procedure failed in two patients due to the poor angle of approach in the axillary area and diffuse severe stenosis in the draining cephalic vein. In eight procedures, sharp needle recanalization was performed under ultrasound guidance, while the other six procedures were performed under fluoroscopic guidance. Chiba and Colapinto needles were used in five and nine procedures, respectively. The mean length of occlusion was 2.7 cm (range 1.8-4.2 cm). There was one case of mild complication, that is, mild contrast extravasation, which was treated by stent deployment. The post-intervention primary patency rates at 6 months, 1 year, and 2 years were 81.8%, 36.4%, and 18.2%, respectively. CONCLUSION: The results of this limited series suggest that the sharp needle recanalization technique is a simple and effective method for the treatment of peripheral non-thrombotic AVF occlusion.

Ultrasound-Guided Deployment of a Plug-Based Vascular Closure Device in Femoral Arteries with Calcified Plaque or Stenosis.

From January 2019 to January 2020, 106 patients (age, 64.8 ± 14.1 years; male, 63.2%) were included to retrospectively investigate the feasibility and safety of ultrasound-guided deployment of ExoSeal after femoral artery access. Baseline characteristics were not different except for age (P = .022), body mass index (P = .009), and diameter (P < .001) between the calcified plaque or stenosis (CS) group (n = 49) and non-CS group (n = 57). The overall technical and clinical success rates were 96.2% and 100%, respectively. The technical (CS group, 48/49; non-CS group, 54/57) and clinical success rates (100%), time to hemostasis (CS group, 3.21 ± 0.54 min; non-CS group, 3.39 ± 0.71 min), and complication rates (CS group, 1/49; non-CS group, 0/57) were not different between the 2 groups. ExoSeal seems to be safe to use under ultrasound guidance in the femoral arteries with CS.

Impact of Superselective Renal Artery Embolization on Renal Function and Blood Pressure.

OBJECTIVES: To evaluate the effect of superselective renal artery embolization in terms of renal function and blood pressure, to compare the results between groups with different embolization extents, and to analyze risk factors of entire study population for postprocedural acute kidney injury (AKI). MATERIALS AND METHODS: The inclusion criteria were patients who underwent renal artery embolization from January 2009 to December 2019, with available serum creatinine and blood pressure data. The exclusion criteria were non-selective embolization of main renal artery, AKI before embolotherapy, and follow-up of less than one month. According to the extent of embolization, the patients were divided into two groups: Group A (1 segment) and Group B (2-4 segments). RESULTS: A total of 48 patients were enrolled. There was a significant difference between pre- and postprocedural estimated glomerular filtration rate (p = 0.030). There were no significant difference between pre- and postprocedural blood pressure. The incidence of postprocedural AKI in group B was significantly higher than that in group A (p = 0.044). There was no significant difference in the incidence of the worsening of hypertension between the two groups. Chronic kidney disease and high embolization grade were predictive for postprocedural AKI (p = 0.012, 0.021). CONCLUSION: Superselective embolization appears to be a safe procedure, but meticulous attention for AKI is required for patients who underwent embolization of more than one segmental artery. An attempt to minimize the extent of devascularization should be pursued to avoid postprocedural complications.

Pharmaceutical Efficacy of Gypenoside LXXV on Non-Alcoholic Steatohepatitis (NASH).

Ginsenosides have offered a wide array of beneficial roles in the pharmacological regulation of hepatic metabolic syndromes, including non-alcoholic steatohepatitis (NASH), non-alcoholic fatty liver disease (NAFLD), and obesity. Of the numerous ginsenosides, Rg3 has been widely investigated, but there have been few studies of gypenosides (Gyp). Particularly, no study on Gyp LXXV has been reported to date. Here, to firstly explore the pharmacological effects of Gyp LXXV against NASH and the related mechanism, methionine- and choline-deficient (MCD) diet-induced NASH mice and hepatic cells (stellate cells, hepatic macrophages, and hepatocytes) were selected. Gyp LXXV exhibited markedly alleviated MCD diet-induced hepatic injury, inflammation, and fibrosis by down-regulating hepatic fibrosis markers such as α-smooth muscle actin(α-SMA), collagen1, transforming growth factors-ß (TGF-ß1), tumor necrosis factor-α (TNF-α), MCP-1, interleukin (IL)-1ß, nuclear factor κB (NFκB), and GRP78. Remarkably, histopathological studies confirmed that 15 mg/kg of Gyp LXXV administration to MCD diet-induced mice led to effective prevention of liver injury, lipid accumulation, and activation of hepatic macrophages, indicating that Gyp LXXV might be a potential anti-NASH drug.

Single-atom catalysts for the oxygen evolution reaction: recent developments and future perspectives.

Single-atom catalysts (SACs) possess the potential to achieve unique catalytic properties and remarkable catalytic mass activity by utilizing low-coordination and unsaturated active sites. However, smaller particles tend to aggregate into clusters or particles owing to their high surface energy. In addition, support materials that have strong interactions with isolated metal atoms, extremely large surface areas, and electrochemical stability are required. Therefore, sufficient information about these factors is needed to synthesize and utilize SACs. Herein, we review the recent investigations and advances in SACs for the oxygen evolution reaction (OER). We present not only the structural characterization of SACs, but also in situ/operando spectroscopic techniques and computational research for SACs to understand the mechanism and reveal the origin of their excellent OER activity. Furthermore, the OER catalytic activity and stability of SACs are summarized to evaluate the current level of SACs. Currently, research on single-atoms as OER catalysts is in the infant stage for synthesis, characterization and mechanism studies. We discuss some challenges for understanding the fundamentals of SACs and enhancing the catalytic performance of SACs for industrial applications.

Electroactivation-induced IrNi nanoparticles under different pH conditions for neutral water oxidation.

Electrochemical oxidation processes can affect the electronic structure and activate the catalytic performance of precious-metal and transition-metal based catalysts for the oxygen evolution reaction (OER). Also there are emerging requirements to develop OER electrocatalysts under various pH conditions in order to couple with different reduction reactions. Herein, we studied the effect of pH on the electroactivation of IrNi alloy nanoparticles supported on carbon (IrNi/C) and evaluated the electrocatalytic activities of the activated IrNiOx/C for water oxidation under neutral conditions. In addition, their electronic structures and atomic arrangement were analyzed by in situ/operando X-ray absorption spectroscopy (XAS) and identical location transmission electron microscopy techniques, showing the reconstruction of the metal elements during electroactivation due to their different stabilities depending on the electrolyte pH. IrNiOx/C activated under neutral pH conditions showed a mildly oxidized thin IrOx shell. Meanwhile, IrNiOx/C activated in acidic and alkaline electrolytes showed Ni-leached IrOx and Ni-rich IrNiOx surfaces, respectively. Particularly, the surface of IrNiOx/C activated under alkaline conditions shows IrOx with a high d-band hole and NiOx with a high oxidation state leading to excellent OER catalytic activity in neutral media (η = 384 mV at 10 mA cm-2) whereas much lower OER activity was reported under alkaline or acid conditions. Our results, which showed that electrochemically activated catalysts under different pH conditions exhibit a unique electronic structure by modifying the initial alloy catalyst, can be applied for the design of catalysts suitable for various electrochemical reactions.