Toward Standardized Photocatalytic Oxygen Evolution Rates Using RuO2@TiO2 as a Benchmark

Hugo A Vignolo-González,Sourav Laha,Alberto Jiménez-Solano,Takayoshi Oshima,Viola Duppel,Peter Schützendübe,Bettina V Lotsch

doi:10.1016/j.matt.2020.07.021

Abstract

SummaryQuantitative comparison of photocatalytic performances across different photocatalysis setups is technically challenging. Here, we combine the concepts of relative and optimal photonic efficiencies to normalize activities with an internal benchmark material, RuO2 photodeposited on a P25-TiO2 photocatalyst, which was optimized for reproducibility of the oxygen evolution reaction (OER). Additionally, a general set of good practices was identified to ensure reliable quantification of photocatalytic OER, including photoreactor design, photocatalyst dispersion, and control of parasitic reactions caused by the sacrificial electron acceptor. Moreover, a method combining optical modeling and measurements was proposed to quantify the benchmark absorbed and scattered light (7.6% and 81.2%, respectively, of λ = 300–500 nm incident photons), rather than just incident light (≈AM 1.5G), to estimate its internal quantum efficiency (16%). We advocate the adoption of the instrumental and theoretical framework provided here to facilitate material standardization and comparison in the field of artificial photosynthesis.

Highlights

Global anthropogenic CO2 emission rates grow at alarming rates
According to literature and our UV-visible (UV-vis) experiments (Figure S3), excessive loading of ruthenium (Ru) species leads to a decrease in overall activity due to the black color of the product that competes with P25 light absorption while producing no reaction.[37,39]
Using a modified photodeposition protocol complemented by colloidal stabilization under the optimized conditions (loading of 0.15 w/w % of Ru(III) to P25, a suspension density of 0.5 mg of P25 per mL of an aqueous solution containing 10 mM KIO3 as sacrificial electron acceptor (SEA) and 1 mM TSPP as a dispersing agent), the collected material can be used as a photocatalytic oxygen evolution reaction (OER) benchmark in an activity screening platform by normalizing the photocatalytic OER rates of an arbitrary sample in an arbitrary setup against this benchmark measured under the same experimental conditions

Summary

Introduction

Global anthropogenic CO2 emission rates grow at alarming rates. Along with increasing the share of renewables on energy portfolios worldwide, it is projected that renewable-to-chemical energy conversion is essential to control the global temperature rise.[1,2,3] In this context, artificial photosynthesis has gained attention in the last decades as it tackles larger-scale solar energy storage by producing chemical fuels such as hydrogen from abundant water and sunlight.[4,5,6] the pinnacle of artificial photosynthesis, namely photocatalytic overall water splitting (POWS), drives an overall thermodynamically uphill chemical reaction using sunlight and involves the kinetically highly challenging water oxidation reaction.

Results

Conclusion