Activity of electrodeposited rhodium in acidic and basic water electrolysis

Hydrogen (H2) is increasingly seen as a future fuel and a potential alternative to fossil fuels, as it is the cleanest and ideal energy carrier. Water electrolysis is one of the easiest methods to produce H2, offering the advantage of simplicity. Rhodium (Rh) is considered one of the best electrocatalysts for water electrolysis. This research was conducted to investigate the activity of electrodeposited Rh for its potential electrocatalytic application in acidic and basic water electrolysis. The electrode was fabricated from a 5 g/L solution of rhodium sulfate [Rh2(SO4)3] electrodeposited at 3.0 V for 3 min in a 92.5% silver (Ag) alloy substrate. Electrochemical characterizations were performed using cyclic voltammetry (CV) and linear sweep voltammetry (LSV) in a three-electrode set-up. The acidic electrolyte was a sulfuric acid (H2SO4) solution while the basic electrolyte was a sodium hydroxide (NaOH) solution. Stability tests were done on a 48-h continuous run of water electrolysis. Results showed onset potentials of 1.4 V and −0.2 V for acidic oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively, while 0.6 V and −0.9 V for basic OER and HER, respectively. A consistent absolute value of limiting current, 8.00 × 10−3 A was observed for both reactions of the two electrolytes. Electrodeposited Rh as an anode showed excellent stability on both acidic and basic media but may fail as a cathode in long-term water electrolysis. The stability was observed to decrease with increasing electrolyte concentration at a higher rate on an acidic medium.