The hydrogen peroxide (H2O2) generation via the electrochemical oxygen reduction reaction (ORR) under ambient conditions is emerging as an alternative and green strategy to the traditional energy‐intensive anthraquinone process and unsafe direct synthesis using H2 and O2. It enables on‐site and decentralized H2O2 production using air and renewable electricity for various applications. Currently, atomically dispersed single metal site catalysts have emerged as the most promising platinum group metal (PGM)‐free electrocatalysts for the ORR. Further tuning their central metal sites, coordination environments, and local structures can be highly active and selective for H2O2 production via the 2e− ORR. Herein, recent methodologies and achievements on developing single metal site catalysts for selective O2 to H2O2 reduction are summarized. Combined with theoretical computation and advanced characterization, a structure–property correlation to guide rational catalyst design with a favorable 2e− ORR process is aimed to provide. Due to the oxidative nature of H2O2 and the derived free radicals, catalyst stability and effective solutions to improve catalyst tolerance to H2O2 are emphasized. Transferring intrinsic catalyst properties to electrode performance for viable applications always remains a grand challenge. The key performance metrics and knowledge during the electrolyzer development are, therefore, highlighted.

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The electrochemical conversion of CO2 affords a sustainable route to produce chemicals and fuels from renewable sources of electricity. Nickel–nitrogen–carbon (Ni–N–C) materials have shown promise in terms of activity and selectivity toward the electro-conversion of CO2 into CO, a feedstock widely used in the chemical sector. Ni–N–C catalysts, postulated to comprise catalytically active atomically dispersed Ni–N x /C sites, are commonly prepared by pyrolyzing a mixture of transition metal-, nitrogen-, and carbon-containing precursors. Herein, we use a zeolitic imidazolate framework (ZIF-8)a subclass of metal organic frameworksas a platform for synthesizing Ni–N–C electrocatalysts. We systematically investigate the role of the Ni concentration impregnated into the ZIF-8 precursor structure during synthesis in the overall structure and performance of the resulting Ni–N–C catalysts for electrochemical CO2 reduction. Our findings show that increased Ni contents in the catalyst precursor results in the formation of Ni-containing particles that increase the catalytic selectivity toward the competing hydrogen evolution reaction, whereas reduced Ni contents preferentially form atomically dispersed Ni–N x /C active sites dispersed in heterogeneous carbon structures consisting of carbon nanotubes and carbonaceous particles. As an optimized concentration of Ni in the precursor mixture, we demonstrate a CO2 reduction selectivity toward CO of ca. 99% Faradaic efficiency at an applied potential of −0.68 V versus the reversible hydrogen electrode.

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Liquid phase Liquid phase fraction 6.85E-04 5.44E-03 Carbon dioxide 1.15E-03 2.81E-03 Nitrogen 8.36E-05 4.76E-05 Methane 0.131573 0.117488 Ethane 2.44E-02 5.57E-02 Propane 3.19E-02 0.131492 iso-butane 2.61E-02 0.126888 n-butane 3.28E-02 0.151564 iso-pentane 4.83E-02 0.131666 n-pentane 3.45E-02 7.28E-02 n-hexane 0.117852 8.18E-02 n-heptane 0.328206 9.09E-02 n-octane 0.209931 3.50E-02 n-nonane 1.32E-02 1.82E-03 c write(iout,5225)(icp,(rmolefr(icp,jph),jph=1,np),icp=1,nc) c End search for sidestreams and begin search for shock wave position c 450 continue c Save position of the last side stream c c ratiolastss=ratiotothroat c write(iout,*) 'end of part 3 kountexpand',kountexpand c c c End search for the sidestream position(s) c ========================================= c c Begin search for the shock wave position c ======================================== c c go to 700 c if (1.d00/arearatio.lt.100.) goto 700 c write(iout,*) c write(iout,*) c write(iout,*) c write(iout,*) 'beginning of part 4 kountexpand',kountexpand c c part 4: find temperature and pressure after jump c ialgo=2 c c iterpath=0 c 470 continue c iterpath=iterpath+1 if (.not.aftershock) then kountexpand=kountexpand+1 endif c c initial guess for the speed after the shock wave c c write(iout,*) 'backpressure,poutspec',backpressure,poutspec c if (kountexpand.le.2) then pshock=poutspec*(rmach**2) tshock=rmach*t fspeedshock=fspeed-vflash/(fspeed*rmmkgmol)* & (pshock-poutspec)/facp c else c pshock=pshockold*(rmach/rmachold)**2 c tshock=tshockold*(rmach/rmachold) c fspeedshock=fspeedshockold*arearatioold/arearatio c endif c write(iout,*) 'set A',vflash,fspeed,rmmkgmol

Further improvements in the performance and cost-effectiveness of water electrolyzers are urgently needed to accelerate decarbonization of hydrogen production. Iridium-free oxygen evolution reaction (OER) electrocatalysts are needed that are active and durable under acidic conditions. Here we report Ru0.6Cr0.2Ti0.2O2, identified from a machine-learning aided density functional theory (DFT) model using Pourbaix decomposition energy and metal-oxygen covalency as descriptors for electrochemical stability. To screen the entire space of bimetallic oxides for stability under harsh acidic conditions, we employ a graph convolution neural network to predict the Pourbaix decomposition energy accurately from unrelaxed structures. This was accomplished with an accuracy of 32 meV/atom. Notably, utilizing an optimized hyperbolic tangent activation function and dropout algorithm reduced the prediction error by 90%. Experimentally, the catalyst has an overpotential of 267 mV at 100 mA/cm2, accompanied by 200 hours of operation with an overpotential increase of less than 5 mV. DFT calculations show that adding Ti into the structure increases the metal-oxygen covalency of the system, improving the stability of the mixed-metal-oxide. At the same time, adding Cr lowers the energy barrier of the HOO* formation rate-determining step, thus improving activity compared to RuO2. We investigate structural and chemical changes during the reaction using in situ X-ray absorption spectroscopy and ptychography-scanning transmission X-ray microscopy. These evidence the evolution of a metastable structure compromised of a strong Ti-oxo network and a hydrous Cr-O passivation layer during the reaction – a structure that slows the dissolution of Ru by 20x while simultaneously suppressing lattice oxygen participation by > 60% compared to the case of RuO2.