Controllable Anchoring of Graphitic Carbon Nitride on MnO₂ Nanoarchitectures for Oxygen Evolution Electrocatalysis

Abstract

The design and fabrication of eco-friendly and costeffective (photo)electrocatalysts for the oxygen evolution reaction (OER) is a key research goal for a proper management of water splitting to address the global energy crisis. In this work, we focus on the preparation of supported MnO 2 /graphitic carbon nitride (g-CN) OER (photo)electrocatalysts by means of a novel preparation strategy. The proposed route consists of the plasma enhancedchemical vapor deposition (PE-CVD) of MnO 2 nanoarchitectures on porous Ni scaffolds, the anchoring of controllable g-CN amounts by an amenable electrophoretic deposition (EPD) process, and the ultimate thermal treatment in air. The inherent method versatility and flexibility afforded defective MnO 2 /g-CN nanoarchitectures, featuring a g-CN content and nano-organization tunable as a function of EPD duration and the used carbon nitride precursor. Such a modulation had a direct influence on OER functional performances, which, for the best composite system, corresponded to an overpotential of 430 mV at 10 mA/cm 2 , a Tafel slope of ≈70 mV/dec, and a turnover frequency of 6.52 × 10 −3 s −1 , accompanied by a very good time stability. The present outcomes, comparing favorably with previous results on analogous systems, were rationalized on the basis of the formation of type-II MnO 2 /g-CN heterojunctions, and yield valuable insights into this class of green (photo)electrocatalysts for end uses in solar-to-fuel conversion and water treatment.

Efficient photoactivated hydrogen evolution promoted by CuxO–gCN–TiO2–Au (x = 1,2) nanoarchitectures

“…1,8,16,18,28 In line with these results, N 1s components (Fig. 2d) were related to bi-coordinated nitrogen (CN–C; VII, BE = 398.7 eV), 4,8,24,28 tertiary N–(C) 3 atoms (VIII, BE = 399.9 eV), 1,8,24,26,28 and –NH x groups (IX, BE = 401.1 eV). 3,16,28,45…”

“…2c), beside the adventitious carbon band (IV, BE = 284.8 eV), 3,9,16,25,28 presented a component at ≈286.1 eV (V) due to both C–O bonds and −C−NH x moieties ( x = 1,2) on gCN heptazine ring edges. 3,4,17,24,44 Finally, signal VI at BE ≈ 288.1 eV was attributed to N–CN carbon atoms in gCN. 1,8,16,18,28 In line with these results, N 1s components (Fig.…”

“…2b) resulted from the concurrence of CuO lattice oxygen (I, BE = 529.9 eV), 21,23 surface chemisorbed –OH groups (II, BE = 531.5 eV), 3,25 and adsorbed water/C–O bonds between gCN and CuO (both contributing to band III, located at BE = 533.0 eV). 10,24 Indeed, –OH presence is beneficial for the target end-use, 1,21 and gCN–CuO bonding is favourable to obtain an improved electron–hole separation, 24 resulting thus in higher functional performances. The C 1s signal (Fig.…”

“…1,13,20 To this aim, graphitic carbon nitride (gCN), a burgeoning n-type semiconductor possessing a two-dimensional structure ( E g ≈ 2.7 eV), presents several concurrent advantages, including cost effectiveness, eco-friendly character, stability, tuneable electronic structure, and attractive photoactivity. 4,11,19,24–27 The system performances can be further improved by the additional introduction of oxide semiconductors and/or metals, obtaining multi-component functional nanoarchitectures. 9,12 In particular, TiO 2 can exert a protective action against Cu x O photocorrosion, limit the undesired recombination of photocarriers affecting gCN, and boost charge mobility at the photoelectrocatalyst–electrolyte interface.…”

Fabrication of p–n Heterostructured Photocatalysts with Triazine-Based Covalent Organic Framework and CuInS2 for High-Efficiency CO2 Reduction

“… In addition, the peaks at 451.9 and 444.4 eV can be attributed to In 3+ 3d 3/2 and 3d 5/2 , respectively, and the S 2p spectrum can be fitted to two peaks at 162.5 and 161.4 eV (Figure e,f), which are assigned to S 2– 2p 1/2 and 2p 3/2 , respectively . After forming a p – n heterojunction in 10 wt % CIS@TCOF, it is noteworthy that the binding energies of Cu 2p, In 3d, and S 2p show a negative shift, while the binding energy of N 1s shows a positive shift, compared with those in pure CIS and TCOF, which is in accordance with the general rule for heterojunction-type photocatalysts. − To determine the direction of the electron transfer during photocatalysis, the in situ irradiated XPS of 10 wt % CIS@TCOF was carried out under light irradiation. Compared with 10 wt % CIS@TCOF in darkness, it can be observed that the C 1s and imine-N 1s peaks of TCOF markedly shift to the low binding energy (Figure b,c), while the Cu 2p, In 3d, and S 2p peaks of the 10 wt % CIS@TCOF composite under light irradiation obviously move toward the high binding energy (Figure d–f), implying that the photogenerated electrons transfer from CIS to TCOF under light irradiation. , Therefore, these XPS results provide important evidence of the photogenerated charge carrier transfer pathway across the CIS@TCOF heterojunction interface.…”